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Full text of "Geology of basement rocks beneath the North Carolina coastal plain"

C.a 



GEOLOGY OF BASEMENT ROCKS BENEATH 

THE NORTH CAROLINA COASTAL PLAIN 

By 

David P. Lawrence and Charles W. Hoffman 

BULLETIN 95 





NORTH CAROLINA GEOLOGICAL SURVEY 

DIVISION OF LAND RESOURCES 

DEPARTMENT OF ENVIRONMENT, HEALTH, 
AND NATURAL RESOURCES 




Photo by Jim Page 



On the cover: 



1. DR-OT-3-65 (6,291 feet) - 384±8 Ma old altered volcanic or gabbroic rock 

2. DR-OT-2-71 (5,805 feet) - fractured coarse-grained granite 

3. ON-OT-1-50 (1,494 feet) - biotite schist (banding is marks from core barrel) 

4. PT-T-1-85 (1,095 feet) - slightly metamorphosed metasiltstone 



The Geological Survey Section examines, surveys, and maps the geology, 
mineral resources, and topography of the state to encourage the wise 
conservation and use of these resources by industry, commerce, agriculture, and 
government agencies for the general welfare of the citizens of North Carolina. 

The Section conducts basic and applied research projects in environmental 
geology, mineral resource exploration, and systematic geologic mapping. 
Services include identifying rock and mineral samples submitted by citizens and 
providing consulting services and specially prepared reports to agencies that 
need geological information. 

The Geological Survey Section publishes Bulletins, Economic Papers, 
Information Circulars, Educational Series and Geologic maps. For a list of 
publications or more information about the Section, contact the Geological Survey 
Section, Division of Land Resources, at Post Office Box 27687, Raleigh, North 
Carolina 27611-7687 or call (919) 733-2423. 



Jeffrey C. Reid 
Chief Geologist 




GEOLOGY OF BASEMENT ROCKS 

BENEATH THE NORTH CAROLINA 

COASTAL PLAIN 

by 
David P. Lawrence and Charles W. Hoffman 



NORTH CAROLINA GEOLOGICAL SURVEY 
BULLETIN 95 

1993 



N.C. DOCUMENTS 

CLEARINGHOUSE 

MAR 7 1994 

N.C. STATE LIBRARY 1 
RALEIGH 



Charles H. Gardner, State Geologist 



STATE OF NORTH CAROLINA DEPARTMENT OF ENVIRONMENT, 

HEALTH, AND NATURAL RESOURCES 
JAMES B. HUNT, JR., GOVERNOR JOHNATHAN B. HOWES, SECRETARY 



Digitized by the Internet Archive 

in 2013 



http://archive.org/details/geologyofbasemen1993lawr 



CONTENTS 



Abstract 1 

Introduction 1 

Methods 2 

Previous work 3 

Basement Surface 4 

Evidence for Early Mesozoic Basins 5 

Geologic map and description of lithologic belts 6 

Carolina Terrane 8 

Spring Hope Terrane 8 

Charleston Terrane 10 

Roanoke Rapids Terrane 10 

HatterasBelt 12 

Metamorphism 15 

Structure 15 

Tectonic Implications 17 

Conclusions 20 

Acknowledgments 21 

References Cited 21 

Appendix A - Basic data for wells and boreholes shown on Plate 1 26 

Appendix B - Thin section descriptions 31 

Appendix C - Photomicrographs of basement samples 42 



TABLES 



Table 1. Abbreviations for county names used in North Carolina Geological Survey 

well coding system 2 

Table 2. Reported isotopic ages of eastern Piedmont and Coastal Plain plutons and 

of eastern Piedmont metamorphism 13 



ILLUSTRATIONS 



Figure. 1 Map showing terrane boundaries and metamorphic grades of crystalline 
rocks beneath the North Carolina Coastal Plain 



Plate 1. Interpretive geologic map of basement rocks beneath the North Carolina 

Coastal Plain in pocket 



Geology of Basement Rocks Beneath the North Carolina Coastal Plain 

By David P. Lawrence 1 and Charles W. Hoffman 2 

1 Department of Geology, East Carolina University, Greenville, NC 27834 

2 North Carolina Geological Survey, Coastal Plain Office, 4100 Reedy Creek Road, Raleigh, NC 27607 



ABSTRACT 

The basement surface beneath the Coastal Plain 
of North Carolina extends from surface outcrop on 
the west, at the eastern edge of the Piedmont 
province, to a maximum drilled depth of 9,854 feet 
below sea level at Cape Hatteras. Cuttings and 
cores from 124 boreholes to basement, combined 
with Bouguer gravity and magnetic maps, permit 
the construction of an interpretive geologic map, a 
structure contour map of the basement surface, and 
a map of metamorphic grade. 

Petrographic study of the cuttings and cores 
indicates that most of the Coastal Plain basement 
consists of rocks similar to those that crop out in the 
Carolina slate belt in the Piedmont — namely slaty 
to schistose metamorphosed mafic, intermediate, 
and felsic tuffs and flows, volcaniclastic mud- 
stones, siltstones, and sandstones, and minor quartz- 
ite. Relatively small bodies of metadiorite, grano- 
diorite, and granite are widely distributed. Under- 
lying the coastal counties from the Virginia line 
south to Onslow County is the Hatteras belt, which 
includes two large composite batholiths informally 
named the Cape Hatteras and Carteret batholiths. 
Another area possibly underlain by a batholith is 
interpreted offshore of Wilmington, but it has not 
been tested by drilling. The Cape Hatteras batholith 
is primarily granite, intruded by gabbroic plutons. 
The Carteret batholith contains diorite, granodior- 
ite, and granite. Marginal to the batholiths in the 
Hatteras belt are schists and gneisses of lower 
amphibolite facies. 

Two late Paleozoic fault zones that crop out in 
the Piedmont, the Nutbush Creek and the Hollister, 



are mappable as magnetic lineaments to the south 
under the Coastal Plain cover. Two east-trending 
faults are inferred to intersect the Hollister fault in 
the Coastal Plain basement. 

No early Mesozoic rift basins have been con- 
firmed under the Coastal Plain, except for exten- 
sions of the Ellerbe, Wadesboro, and Sanford ba- 
sins; however, the margin of a minor basin has been 
interpreted by some authors to lie beneath Cape 
Hatteras and the inner continental shelf sediments. 

Recent tectonostratigraphic terrane descriptions 
and plate tectonic speculations are consistent with 
the interpretations presented in this report; some 
terrane boundaries are better constrained as a result 
of this analysis. 

INTRODUCTION 

The composition and structure of basement 
rocks, namely Pre-Mesozoic crystalline rocks and 
early Mesozoic (Upper Triassic to Lower Jurassic) 
rift basin sedimentary rocks, beneath the Early 
Cretaceous and younger sedimentary rocks that 
comprise the North Carolina Coastal Plain have 
been the subject of geologic speculation and inves- 
tigation for nearly 100 years. There are numerous 
scientific and practical reasons for such efforts. 
The recognition and delineation of faults or fault 
systems within the Coastal Plain basement might 
provide a better understanding of factors that con- 
trolled deposition and subsequent faulting in the 
overlying sedimentary section. The overlying sedi- 
mentary rocks host and control movement of the 
groundwater of the Coastal Plain region. Thus, 
increased knowledge of the thickness of the sedi- 



mentary section and the presence and location of 
major discontinuities is important. 

The availability of rock material to be quarried 
as crushed stone is important to the economic 
development of the Coastal Plain region. Several 
quarries are currently being operated where Coastal 
Plain cover of suitable granitic rock is thin. Other 
areas with the potential for crushed stone resources 
may be delineated through research on the base- 
ment rocks. Oil and gas exploration in the Coastal 
Plain has thus far been unsuccessful. Confirmation 
of the presence and location of one or more early 
Mesozoic rift basins beneath the Coastal Plain may 
revive interest in exploring for oil and gas. Knowl- 
edge of the Coastal Plain basement rocks will 
certainly improve our understanding of the tec- 
tonic and geologic history of the continental mar- 
gin. When data from the Coastal Plain basement 
rocks are linked with data from the Piedmont 
region and put in the context of the Atlantic conti- 
nental margin, we will be better able to unravel the 
events that shaped the region. 

Most previous studies used drill-hole informa- 
tion for limited parts of the Coastal Plain; others 
primarily made use of geophysical data. Daniels 
and Zietz (1978), Daniels and Leo (1985), Thomas 
and others, (1989), and Horton and others (1989) 
used both drill-hole information and geophysical 



data, but on a regional scale. This paper synthe- 
sizes the best available basement lithologic infor- 
mation from a widespread sampling of basement 
materials and attempts to describe the distribution 
of rock types by interpreting the lithologic data in 
light of regional geophysical (magnetic and grav- 
ity) data. This study relies sparingly on basement 
depths or lithologies reported in the literature. 
Many earlier studies conflict either internally, with 
other reports, or with observations of original 
samples and logs made as part of this study. Ancil- 
lary data from the literature such as radiometric 
dates are considered in this study. 

METHODS 

Basement material recovered from samples of 
124 boreholes provides the primary database used 
in this study. The geologic data in this report were 
derived from cuttings and cores from boreholes 
made for water wells, petroleum and other mineral 
exploration, and stratigraphic tests within the 
Coastal Plain region. Samples from such drilling, 
when available, have been collected and main- 
tained by the North Carolina Geological Survey 
(NCGS). With three exceptions, boreholes, oil test 
wells, and auger holes discussed herein are referred 
to by their NCGS well code, a four-element code 
beginning with a two-letter abbreviation of the 
county (Table 1) in which the well is located 



Table 1 . Abbreviations used for county names in North Carolina Geological Survey well coding system. 



BF Beaufort 

BT Bertie 

BL Bladen 

BW Brunswick 

CM Camden 

CR Carteret 

CH Chowan 

CU Columbus 

CN Craven 

CD Cumberland 

CK Currituck 



DR Dare 

DP Duplin 

ED Edgecombe 

GA Gates 

GR Greene 

HA Halifax 

HR Harnett 

HT Hertford 

HO Hoke 

HY Hyde 

JH Johnston 



JO Jones 

LN Lenoir 

MR Martin 

MO Moore 

NA Nash 

NH New Hanover 

NO Northampton 

ON Onslow 

PA Pamlico 

PS Pasquotank 

PE Pender 



PQ Perquimans 
PT Pitt 
RI Richmond 
RO Roberson 
SA Sampson 
SC Scotland 
TY Tyrell 
WA Washington 
WY Wayne 
WS Wilson 



(Hoffman and Nickerson, 1988). Holes not in- 
cluded in the NCGS database but referenced herein 
and shown on Plate 1 were drilled and reported on 
by researchers at Virginia Polytechnic Institute and 
State University (Becker, 1980; Pratt and others, 
1985; Farrar, 1980b) and are referred in this report 
as VPI-1, VPI-2, and VPI-3. See Appendix A for 
basic information on the borehole data. 

The magnitude and shape of a magnetic anomaly 
will always be a function of the relative magnetic 
susceptibilities of adjacent rock masses; thus, there 
can be no absolute rules for interpretation and rock 
lithologies interpreted exclusively from magnetic 
data are merely approximations (Stoddard and 
others, 1991). The following characteristics of 
magnetic anomalies were used to interpret the 
geologic units shown on Plate 1 : 

• Gabbro and metagabbro were interpreted in 
regions of 700- to 1000-gamma anomalies that 
were equant to lozenge shaped. 

• Mafic volcanics are inferred in regions of 
elongate anomalies of 300 to 500 gammas. 

• Felsic to intermediate plutonic regions are 
inferred by a lack of strong linear anomalies; dior- 
ite or granodiorite plutons are suggested by circu- 
lar 400-gamma positive anomalies and granite by 
200- gamma positive anomalies. If granite is sur- 
rounded by mafic rocks, the pluton will show a 
broad, low-relief magnetic low. 

• Intermediate volcanics are shown in areas of 
200- to 400-gamma elongate anomalies, and felsic 
volcanics as strings of 100- to 300-gamma anoma- 
lies. 

• Muscovite schists are differentiated from 
higher iron content biotite schists by a difference of 
about 200 gammas. 

• Faults are indicated on the basis of truncated 
anomalies, offset anomalies, apparent drag folds, 
and sudden changes in magnetic anomaly shapes, 
patterns, or overall magnetic level along prominent 
lineaments. 

Thin sections made of chips picked from cut- 
tings or from slabs of cores were examined petro- 



graphically (see Appendix B for thin section de- 
scriptions and Appendix C for photomicrographs 
of representative basement lithologies and tex- 
tures). Sample lithologies were then plotted at their 
well locations on l:500,000-scale aeromagnetic 
(Zietz and others, 1984) and Bouguer gravity maps 
(Black, 1986; Daniels and Leo, 1985). Contactsfor 
inferred map units were determined by correlating 
lithologies known from wells with magnetic and 
gravity anomalies. Where samples were not avail- 
able from a given map unit, the lithology was 
inferred from the intensity and geometry of the 
magnetic anomaly. 

In general, the gravity data points are spaced so 
far apart and the basement is so deep that most 
small units cannot be resolved. Elongate positive 
gravity anomalies of 20 milligals were assumed to 
indicate possible belts of mafic volcanics. The 
Cape Hatteras granite batholith is marked by a 40- 
milligal negative gravity anomaly and the Rocky 
Mount granitic pluton is marked by a 10- to 14- 
milligal negative anomaly. 

Geologic maps (Burt and others, 1978; 
Campbell, 1984; Farrar, 1985a, 1985b; Kite and 
Stoddard, 1984; Boltin and Stoddard, 1987; Horton 
and Stoddard 1986; Waskom and Butler, 1971; 
Wilson, 1979, 1981; Wilson and Spence, 1979; and 
North Carolina Geological Survey, 1985) of the 
eastern Piedmont area were used to correlate units 
that extend beneath the Coastal Plain. Many areas 
exhibiting magnetic and gravity anomalies were 
not penetrated by drilling so their similarities to 
anomaly signatures of known rock units were used 
for correlation purposes. 

PREVIOUS WORK 

Numerous studies have drawn conclusions 
about the composition and structure of basement 
rocks beneath some or all of the North Carolina 
Coastal Plain. In addition to those described be- 
low, examples include Johnson (1907), Ferenczi 
(1959), Brown and others (1972), Becker (1981), 



Russell and others (1980), Russell, Speer, and 
Russell (1985), Lyke and Winner (1986), and 
Klitgord and others (1988). Most basement studies 
used well records for limited parts of the region or 
made use of geophysical data and limited well data. 
Other authors speculated on regional belts or trends 
in the southeastern United States or the plate tec- 
tonic origins of such features. 

The earliest substantive studies of the Coastal 
Plain basement were by Spangler ( 1 950) and S keels 
(1950). Their reports were generated from geo- 
logical and geophysical data, respectively, devel- 
oped through active oil and gas exploration in 
eastern North Carolina. These investigators inter- 
preted a basement of complex composition with a 
structural grain trending approximately north- south. 

Richards (1954) examined lithologic data from 
a Camden County oil test well (CM-OT-1-53) and 
suggested a possible buried Triassic basin. Daniels 
and Zietz (1978) interpreted subsequently gener- 
ated regional magnetic data and inferred a large 
Triassic rift basin through the central Coastal Plain. 
Sampair (1979) specifically investigated this mag- 
netic anomaly with additional geophysical surveys 
and with several drill holes to basement. He found 
no Triassic or Jurassic sedimentary rocks beneath 
the Cretaceous section and interpreted the mag- 
netic anomaly as a Precambrian or early Paleozoic 
basin or synform containing up to 7,000 feet of 
metasedimentary rocks. 

Bonini and Woolard (1960) produced a geo- 
logic sketch map based on extensive seismic re- 
fraction data from the Coastal Plain and adjacent 
Piedmont as well as rock types found in several 
wells. Their work represents one of the earliest 
attempts to map lithologic regions under the Coastal 
Plain. They concluded that lithologic and struc- 
tural trends within the basement rocks were essen- 
tially the same as those of the Piedmont region. 

Burt and others (1978) mapped the distribution 
of Jurassic diabase dikes in the Piedmont and 



beneath the Coastal Plain cover. This work relied 
on magnetic anomalies to map dikes where cov- 
ered or where not confirmed by field mapping. 

Daniels and Zietz (1978) presented a prelimi- 
nary geologic map of the Coastal Plain basement 
based on partial aeromagnetic coverage and drill 
data. Pratt and others (1985) published a paper on 
basement rocks of the Lumberton area in Robeson 
County. This study is an important contribution 
because the structure below the basement surface 
was determined by both seismic and gravity meth- 
ods. 

Daniels and Leo (1985) presented a map of the 
basement rocks of the Atlantic Coastal Plain, based 
on descriptions of cores and cuttings and on inter- 
pretation of Bouguer gravity anomalies. Thomas 
and others (1989) summarized much of the same 
data for their map of the subsurface Appalachians. 
In the offshore region, Hutchinson and others (1982) 
studied the top of basement structures and included 
some interpretation of the basement rock types 
from magnetic and seismic studies. 

BASEMENT SURFACE 

The altitude of the basement surface relative to 
mean sea level is shown on Plate 1 . The basement 
surface is defined as the base of the Upper Meso- 
zoic to Lower Cretaceous sedimentary section 
which is commonly referred to as the post-rift 
unconformity surface. Basement surface eleva- 
tions were determined from geophysical log inter- 
pretations and from sample information. The 174 
data points used to produce the map provide only a 
generalized structure contour map. 

The basement surface has been mapped at a 
higher resolution in limited areas. Almy (1987) 
used multi-channel seismic reflection data from 
the area of Pamlico and Albemarle Sounds to 
produce a 1 : 125,000 scale map of basement with a 
100-foot contour interval. Several northeast- south- 
west trending faults with offsets of 100 to 200 feet 




were mapped by Almy through this region. Un- 
published data in the the North Carolina Geologi- 
cal Survey files (North Carolina Oil and Gas, 1966) 
include maps of the basement surface in portions of 
Onslow, Pender, New Hanover, and Brunswick 
counties. These maps, with a contour interval of 25 
feet and a scale of 1:62,500, are based on the then 
available drillhole data and seismic reflection data. 
Limited and very minor faulting is depicted on this 
data set. The structures and the contours inter- 
preted by Almy (1987) and in the unpublished data 
set are generalized for presentation on Plate 1. 

Beneath the southern part of the Coastal Plain, 
the structure contours define a very broad, south- 
east-plunging positive feature known as the Cape 
Fear arch. To a lesser degree, the Norfolk arch 
(Fort Monroe high), which approximately coin- 
cides with the Virginia-North Carolina State Line, 
is apparent from the -2,000-foot and deeper con- 
tours. The intervening area of deeper basement and 
thicker sedimentary section between these two 
featurers is known as the Albemarle embayment. 

Several minor positive features are defined 
beneath the upper Coastal Plain by the drillhole 
data of this report and from literature sources. The 
most prominent paleotopographic feature is the 
granitic monadnock which crops out at an eleva- 
tion of approximately 90 feet above sea level near 
Fountain, Pitt County. A similar though smaller 
amplitude feature is present south of the Fountain 
pluton beneath the Greene-Lenoir County line. 
Sparse cuttings in the lowermost sample from a 
single Greene County borehole, GR-T-1-68, indi- 
cate this feature to be an altered medium-grained 
plutonic rock. Paleotopographic highs of base- 
ment material also crop out within the Coastal 
Plain west of Goldsboro, and in several localities in 
Johnston and Harnett counties (North Carolina 
Geological Survey, 1985). The -400-foot contour 
through Bladen and Robeson counties defines two 
ravinements in the basement surface more or less 
coincident with the courses of the modern Cape 
Fear and Lumber Rivers. 



EVIDENCE FOR EARLY MESOZOIC 
BASINS 

Many authors have speculated on the existence 
of early Mesozoic sedimentary rift basins beneath 
the North Carolina Coastal Plain. The Ellerbe, 
Sanford, and Wadesboro basins, which crop out in 
the Piedmont, have been confirmed by drilling to 
continue under the western Coastal Plain (Daniels 
and Leo, 1985). 

Daniels and Zietz (1978) suggested the exist- 
ence of a large buried Triassic basin east of 
Greenville and Kinston on the basis of a rapid 
increase in depth to magnetic sources. Sampair 
(1979) reported results of drilling and geophysical 
surveys which indicated that no Triassic basin lay 
in the area, but instead that a thick section of low 
greenschist facies phyllite was present. Drill holes 
CN-T- 1 -79, PT-T- 1-85, BF-OT-4-63, and BF-OT- 
1-63 all lie within the area of the proposed basin, 
and all penetrated phyllitic metasedimentary rocks. 
Bonini and Woolard (1960) found one area to the 
northeast of Fayetteville in Johnston County, and 
another near Raeford in Hoke County where sub- 
Cretaceous rocks had atypically low refraction 
seismic velocities, and concluded that Triassic 
rocks might be present. No Triassic rocks have 
been drilled in the area, and Cumberland County 
wells CD-T-3-XX, CD-P-1-67, CD-T-3-68, and 
CD-T- 1 -86 all encountered phyllite, metasiltstone, 
and metagraywacke. Such a suite of rocks might 
have a lower refraction seismic velocity than other 
parts of the basement richer in metavolcanic and 
metaplutonic rocks. 

Richards (1954) reported several thousand feet 
of Triassic rocks drilled in Camden County well 
CM-OT-1-53 and interpreted the existence of a 
buried Triassic basin in the area. He described red 
sedimentary rocks, green chert, and diabase. On 
the basis of Richards' report and on the basis of 
reported red sandstone, siltstone and olivine dia- 
base in Pasquotank County well PS-OT- 1-71, Olsen 
and others ( 1 99 1 ) suggested that an early Mesozoic 



rift-basin probably exists beneath the northeastern 
North Carolina Coastal Plain and informally named 
it the Elizabeth City basin. Horton and others 
(1991) show an Elizabeth City basin on their ter- 
rane map, as well as small areas of Triassic rocks in 
Gates and Columbus counties. 

We re-examined the evidence for a buried rift 
basin beneath the northeastern Coastal Plain. The 
samples from CM-OT-1-53 indicate that 
greenschist-facies, pale-green metarhyolite was 
penetrated at an approximate depth of 2,830 feet 
and continued to 4,410 feet. From this depth to 
5,700 feet most of the chips are composed of 
diabase; and below 5,700 feet to 6,420 feet the 
crystalline material is highly contaminated with 
sediments from uphole. At 2,796 feet in a nearby 
well, CM-OT-1-65, metarhyolite nearly identical 
to that observed in CM-OT-1-53 was penetrated 
and recovered by conventional coring. Sediments 
above the metarhyolite in CM-OT-1-65 are prob- 
ably all Cretaceous and younger in age, although 
Brown and others (1972) identify the updip feather 
edge of their unit H, in part possibly latest Jurassic 
age but not of rift basin orig in, immediately above 
basement. 

Well PS-OT-1-71 penetrated diabase at 2,596 
feet. A few chips from above the diabase are red 
siltstones of undetermined age but are typical of 
basal Cretaceous sediments in the region. A posi- 
tive magnetic anomaly approximately half-way 
between the Camden County wells and the 
Pasquotank County well could be due to a diabase 
sheet. Thus, Richards' (1954) section of Triassic 
rocks does not exist and reddish sediments in other 
wells of the area have been systematically corre- 
lated downdip with Coastal Plain sedimentary units. 
Undeniably, a significant Jurassic diabase body 
seems to be present in the Pasquotank-Camden 
County area. Although a small early Mesozoic rift 
basin can not be unequivocally eliminated from the 
vicinity of the Pasquotank County well, the weight 
of the evidence is against the existence of a rift 
basin within Coastal Plain basement here. 



While small early Mesozoic rift basins might 
remain to be discovered beneath the Coastal Plain, 
none have been proved to date. Drilling has yet to 
confirm any such basins. To the contrary, drilling 
has repeatedly refuted the existence of proposed 
basins. Seismic reflection data may be the best data 
source to address the existence of rift basins be- 
neath the Coastal Plain, since this data type has 
successfully located basins in other parts of the 
eastern U.S. and offshore (Hutchinson and Klitgord, 
1988; Klitgord and Hutchinson, 1985). However, 
such data for the North Carolina Coastal Plain are 
limited or of a proprietary nature. 

In the offshore, seismic surveys have identified 
numerous basins (Hutchinson and others, 1982; 
Benson, 1984). Brown and others (1972) reported 
shale and feldspathic sandstone (their unit I) from 
9, 145 to 9,853 feet in the Hatteras Light well (DR- 
OT-1-46), which they provisionally judged to be 
Late Jurassic in age. Manspeizer and Cousminer 
(1988) indicate the possibility of an early Meso- 
zoic rift basin at Cape Hatteras, as well as one just 
offshore of Albermarle sound. Klitgord and others 
(1988) interpret an early Mesozoic basin on U.S. 
Geological Survey seismic line 32 just offshore of 
Cape Hatteras and include the 800 feet of sand- 
stone above basement in DR-OT- 1 -46 as part of the 
sedimentary section in the basin. Without age data 
on the basal Hatteras well sediments and without a 
seismic tie from the well to the offshore data, 
assignment of these beds to an early Mesozoic rift 
basin depositional setting remains speculative. 

GEOLOGIC MAP AND DESCRIPTION OF 
LITHOLOGIC BELTS 

Lithologic characteristics and tectonic features 
of the basement rocks beneath the North Carolina 
Coastal Plain provide the basis to group them into 
five major regions (Figure 1). These regions gen- 
erally coincide with several terranes named by 
Horton and others (1989) and Horton and others 
(1991). Although these terrane names are used 
herein as a matter of convenience, this report pro- 



vides substantially more definition to and docu- 
mentation of these regions than has been previ- 
ously presented. The five regions presented and 
discussed in the following text are: 

• Carolina terrane (Carolina Slate belt area 
west of Nutbush Creek fault zone) 

• Spring Hope terrane (area south of the 
Goochland terrane which lies between the Nutbush 
Creek fault zone and the Hollister fault zone), 

• Charleston terrane (area south of the inferred 
Pender fault zone), 

• Roanoke Rapids terrane (area east of the 
Hollister fault zone extending to the coastal schist 
and batholith belt and north of the inferred Pender 
fault zone), and 

• Hatteras belt (coastal batholith and schist 
belt). 



tion is relatively homogeneous and there is little 
mafic rock present. 

The small 430±13 Ma (Rb/Sr) Lemon Springs 
granite pluton (Campbell, 1984; Campbell and 
Kish, 1989) is found within this terrane at the 
feather edge of the Coastal Plain, as is the Millstone 
Lake biotite granitoid northeast of Lilesville 
(Fullagar and Butler, 1979; Evans and Speer, 1984). 
Neither of these bodies is obvious on the basis of 
the geophysical data. Thus, other granitic plutons 
might be present within the Carolina terrane; but if 
so, they are undetected because of a lack of drill 
holes. Such rocks would likely show little mag- 
netic contrast with the surrounding felsic volcanics 
and metamorphosed volcaniclastic sedimentary 
rocks, due to similar low magnetic susceptibilities. 



The Carolina terrane as used in this report 
includes the Albemarle arc, Crabtree terrane, and 
the Falls Lake terrane of Horton and others (1991). 
The tentatively named Spring Hope and Roanoke 
Rapids terranes are both bounded by high-angle 
faults, and may just be fault blocks of adjacent 
terranes. The Hatteras belt may be a separate 
terrane, or just the higher-grade part of the Roanoke 
Rapids terrane. 

Carolina Terrane 

Carolina slate belt rocks underlie the 
westernmost Coastal Plain in Harnett, Richmond, 
Moore, Hoke, and Scotland counties. The database 
coverage in this region is sparse, with only six 
wells containing basement samples. Basement 
rock in MO-T-1-86 is a biotite-muscovite-plagio- 
clase-quartz schist, probably derived from a 
graywacke. HR-A-4-83 and MO-T-1-83 contain 
white mica phy llite. The rest of this region is likely 
to be underlain by metamorphosed volcaniclastic 
sedimentary rocks and intermediate to felsic 
volcanics in the chlorite and biotite zone of the 
lower greenschist facies of regional metamorphism. 
The area is one of low magnetic values and little 
magnetic anomaly relief, suggesting that the sec- 



Several north-trending Jurassic diabase dikes, 
visible on the magnetic map as narrow positive 
anomalies and shown on the geologic map of North 
Carolina (North Carolina Geological Survey, 1985) 
and by Burt and others (1978), also occur within 
the region. The ages of these dikes probably fall in 
either the 195+5 Ma or the 175+5 Ma Jurassic 
magmatic episodes (deBoer and others, 1988). 

This region is part of the Carolina slate belt, but 
most of the available well data lie east of the large 
positive gravity anomaly that characterizes the 
Carolina slate belt. The lithologies in this area may 
thus be somewhat less mafic and dense than in the 
exposed Carolina slate belt. Rocks in the wells are 
either of volcaniclastic sedimentary or felsic volca- 
nic origin and the magnetic and gravity anomalies 
are lower than in most of the adjacent exposed slate 
belt. 

Spring Hope Terrane 

This area stretches from Warren County in the 
north to Bladen and Robeson counties in the south. 
Where the Hollister fault zone extends to the south 
under the Coastal Plain cover (Figure 1 ), the branch 
that continues straight south and intersects the 



8 



inferred Pender fault is chosen as the eastern bound- 
ary of the Spring Hope Terrane. In the northern end 
of this terrane there are outcropping Piedmont 
rocks that have been mapped by Farrar (1985a, 
1985b), Boltin and Stoddard (1987), and Wilson 
and Carpenter (1975). Farrar (1985a) named the 
exposed portion of this area between the Nutbush 
Creek and Hollister fault zones the Raleigh block. 
The Raleigh block is composed of Raleigh belt and 
Eastern slate belt rocks and includes the Goochland 
terrane (Farrar, 1985a, and Horton and others, 
1989). This exposed part of the Piedmont includes 
extensive amphibolite-facies Precambrian gneiss 
and schist (Goochland terrane) and granitic plutons 
in the core of the Wake-Warren antiform. 
Greenschist-facies-metamorphosed intermediate to 
felsic volcanics and metasedimentary rocks occur 
in the eastern and southern parts of the exposed 
area (Spring Hope terrane). 

In the southern extension of the Raleigh block, 
beneath Coastal Plain cover, minor quantities of 
undivided felsic, intermediate, and mafic volcanic 
units occur as extensions of units mapped by Farrar 
in the exposed area. Boreholes CD-P- 1-67, CD-T- 
3-68, and SA-T-1-86 were all drilled into a large 
magnetically quiet area in Sampson, Cumberland, 
and part of Hoke counties consisting of locally 
phyllitic metamudstones and metagraywacke that 
possibly correlate with Farrar's (1985b) Spring 
Hope formation (informal name). This area of 
metasedimentary rocks ranges from 58 to 13 km 
across. 

South of the magnetically quiet area is a com- 
plex region of narrow, alternating high and low 
magnetic anomalies. This region is centered around 
Lumberton in Robeson County and extends east- 
ward to the Hollister fault zone. Magnetic trends 
within this region align northeast- southwest to 
east-west. The linear magnetic highs are inter- 
preted to reflect mafic and intermediate 
metavolcanic rocks and the magnetic lows are 
interpreted to reflect felsic metavolcanic and 
metasedimentary rocks. 



The Lumberton borehole (VPI-2) described by 
Becker (1980) and Pratt and others (1985) pen- 
etrated interlayered felsic and mafic metavolcanic 
rocks metamorphosed to lower amphibolite facies. 
The volcanic sequence found in the hole was ob- 
served on a nearby seismic line to dip southeast at 
about 20 degrees and there is a suggestion of a 
syncline on the southeast end of the seismic line. 

To the north of the Lumberton hole, phyllitic 
meta-tuf f is found in RO-T-2-68 . In Wayne County, 
east of the metamudstone belt and near the Hollister 
fault zone, a unit of mixed metavolcanic rocks is 
evidenced by metamorphosed mafic and interme- 
diate volcanics found in WY-T-4-88, WY-T-3-86, 
and WY-T-2-86. In Bladen and Pender counties, in 
the southeastern part of the region, probable 
metasiltstone is found in BL-T-2-84, while two 
holes, BL-OT-1-59 and PE-OT-1-59, contain ma- 
fic metavolcanic rocks. Metamorphic grade is 
higher across the southern part of this block than 
through the central part; the metavolcanic rocks in 
Robeson County drill hole VPI-2 have reached 
lower amphibolite facies, since the mafic rocks 
contain oligoclase and hornblende (Becker, 1980). 
The rocks underlying Bladen County contain bi- 
otite, and are coarser and more schistose than those 
to the north beneath Sampson and Cumberland 
counties, where only chlorite and white mica have 
been found. 

Plutons appear to be rare in the Coastal Plain 
region between the Hollister and the Nutbush Creek 
fault zones. The small Lillington pluton crops out 
and is quarried in the western part of the area (Kish, 
1983). A metatrondhjemite body, probably a 
subvolcanic pluton, crops out near Fuquay- Varina 
(Farrar, 1985a; McSween and others, 1991). The 
only other known pluton is the roofed granite that 
causes the negative gravity anomaly near 
Lumberton (Pratt and others, 1985). A few narrow, 
northwest-trending positive magnetic anomalies 
indicate the presence of Jurassic diabase dikes in 
the northern part of this region. None are evident 
in the southern part of the region. This may simply 



be the result of masking of short wavelength anoma- 
lies by the increased distance to magnetic source 
beneath Coastal Plain cover. 

Charleston Terrane 

In this most southern part of the Coastal Plain 
(New Hanover, Columbus, and Brunswick coun- 
ties), magnetic trends are east-west to northeast- 
southwest. Magnetic anomalies indicate that base- 
ment of this area consists mainly of 
metasedimentary rocks and f el sic metavolcanic 
rocks, with only minor intermediate or mafic 
metavolcanic rocks, and one large mass of 
metabasalt or metagabbro. 

Samples from BW-OT- 1 -7 1 are poorly phyllitic 
with fine-grained white mica. The protolith was 
apparently a lapilli tuff; no relict crystals are present. 
A medium-grained (1-2 mm grain size) diabase 
was recovered from CU-T-2-76. This sample is 
distinctly unmetamorphosed and may be from a 
Jurassic diabase sheet or dike. Within this region, 
two wells are sited in areas of low magnetization. 
One, BW-T-1-73, contains quartzite. The other, 
NH-OT-1-66, penetrated poorly phyllitic 
metamudstone and altered mafic volcanic rocks. 

Amphibolite-facies, hornblende-bearing rocks 
are found in boreholes BW-T- 1 -79 and PE-T- 1-83, 
though nearby wells PE-OT-4-66 and NH-OT-1- 
66 contain felsic, intermediate, and mafic 
metavolcanic rocks at greenschist grade. The rela- 
tionships here are unclear. Daniels and Leo ( 1 985) 
included the amphibolite-facies rocks in a continu- 
ous higher grade belt near the coast. Horton and 
others (1989) included these rocks in their higher 
grade Hatteras terrane. This small belt of higher 
grade rocks is shown on Plate 1 separated from the 
lower grade rocks to the west by an inferred thrust 
fault since the metamorphic grade and magnetic 
trends of this area are anomalous. No aeromag- 
netic or gravity trends, however, specifically coin- 
cide with this inferred fault. 



An unnamed batholith is inferred from a large 
and intense (-50 milligals) gravity low in the area 
offshore of Cape Fear (Hutchinson and others, 
1982). Although no drilling has penetrated base- 
ment in this area, the distinctive gravity signature 
and alignment with similar features to the north 
strongly supports interpretation of a batholith in 
the subsurface of this area. 

Roanoke Rapids Terrane 

This area extends from the Virginia state line 
from Northampton County to northern Camden 
County to the inferred Pender fault zone in the 
south. Immediately east of the Hollister fault zone, 
the magnetic anomalies closely resemble those of 
the Carolina slate belt north of Durham. Thus, the 
geologic section is inferred to be somewhat similar 
to that described for the northern slate belt by 
Harris and Glover (1988). 

There are a few outcrops near the towns of 
Wilson, Rocky Mount, Halifax, and Roanoke Rap- 
ids, but the rest of the basement in this region is 
covered by Coastal Plain sediments. The 
Contentnea Creek granite crops out south of the 
town of Wilson (Farrar, 1985a; 1985b). The Rocky 
Mount granite-diorite pluton crops out in the west- 
ern part of Wilson (Farrar, 1980b, 1985a; 1985b; 
Moncla, 1990, Spruill and others, 1987). The 
Halifax County complex, mafic and ultramafic 
rocks interpreted to be a small ophiolite slice, crops 
out in stream valleys north of the Rocky Mount 
pluton (Kite and Stoddard, 1984). 

North of the Halifax County complex lies the 
Butterwood Creek granite, metavolcanic rocks and 
metasedimentary rocks of the Easonburg forma- 
tion, and the Roanoke Rapids complex (Horton and 
Stoddard, 1986; Farrar, 1985a, 1985b; Boltin and 
Stoddard, 1987). As named by Farrar (1985b), 
metasedimentary rocks of the Easonburg forma- 
tion (Farrar, 1985b) overlie the Roanoke Rapids 
complex in Halifax and Northampton counties. 
Intrusive rocks of the Roanoke Rapids complex 



10 



include trondhjemite, quartz diorite, and quartz 
keratophyre. Layered rocks include felsic to inter- 
mediate plagioclase-crystal and crystal-lithic 
metatuffs, with volumetrically less important 
quartz-mica phyllites and volcaniclastic 
metagraywacke. The Easonburg formation in- 
cludes interlayered metagraywacke, metasiltstone, 
metamudstone, metaconglomerate, and intermedi- 
ate and felsic metavolcanic rocks. 

To the east, at Fountain in Pitt County, an early 
Paleozoic pluton rises as an erosional monadnock 
about 350 feet above the surrounding basement 
surface and crops out within the Coastal Plain. 
This peralkaline granite is metamorphosed to lower 
amphibolite fades (Mauger and others, 1983; 1987). 
Subsurface data indicate that other plutons in this 
region include: a small metamorphosed body of 
granite and granodiorite in Northampton County 
(NO-T-3-66 and NO-T-2-66); a small metagranite 
body at the town of Halifax (HA-A-1-84); two 
small metatonalite bodies near Goldsboro (WY-T- 
1-82 and WY-T-2-82); a metagrabbro body in 
Greene County (GR-T-1-68); and a granodiorite- 
quartz monzonite-aplite body in Lenoir County 
(LN-T-1-86, LN-T-2-86, and LN-T-3-86). 

The rocks between the Hollister fault zone and 
a north-south line approximately through Greenville 
(central Pitt County) are layered and consist largely 
of felsic to mafic metavolcanic rocks, with 50 
percent or less of the section made up of 
metamudstone, metasiltstone, and volcaniclastic 
metasandstones. 

In a belt east of Greenville, metamudstones and 
metasandstones make up more than 50 percent of 
the section, and metavolcanic rocks are subordi- 
nate. The boundary between the volcanic-rich sec- 
tion and the volcanic -poor section was in the past 
interpreted as the boundary of a Triassic basin 
(Daniels and Zietz, 1978). More recently, Daniels 
and Leo (1985) interpreted this magnetic linea- 
ment to be a possible fault (see Structure section 
below). North of Greenville, intermediate crystal 



metatuff is found in BT-T- 1-82 and quartz-sericite 
phyllite that might be a felsic metavolcanic rock 
but is more likely a metasiltstone, occurs in HA-T- 
1-85 in southeastern Halifax County. North and 
west of Fountain, the rocks lie in the biotite zone 
and recrystallization has been too extensive to 
allow clear determination of protolith. A gneissic 
rock, probably a metasandstone, is found in ED-T- 
1-82 and phyllitic metamudstone and mica schist 
occur in WS-T-1-86 and WS-T-2-86. 

Southwest of Greenville, the rock types are 
similar to those found to the north. The area 
contains interlayered metasedimentary rocks and 
felsic to mafic metavolcanic rocks. WY-T-3-84 
contains fine-grained quartzite, sericite phyllite, 
and metasiltstone; LN-T-2-85 penetrated a phyllitic 
felsic metatuff, and DP-T- 1-79 drilled into phyllitic 
intermediate metavolcanic rock. Two wells pen- 
etrate the center of a 110-km-long magnetic unit 
that trends about N300E through Pitt, Lenoir, and 
Duplin counties; LN-T- 1-79 contains a greenstone, 
probably metabasalt, and DP-T- 1-79 contains in- 
termediate metavolcanic rock. Units in the south- 
ernmost part of this block include biotite schist in 
DP-T-2-82 and two mica schist in ON-OT-1-50. 
Just west of the Carteret batholith, in Jones and 
Onslow counties, sericite-, chlorite-, or biotite- 
bearing felsic metavolcanic rocks and volcaniclastic 
metasiltsones, metasandstones, and minor meta- 
morphosed intermediate volcanic rocks occur in 
wells JO-OT-1-60, ON-OT-1-59, ON-OT-2-60, 
ON-OT-2-67, and surrounding nearby wells. ON- 
OT-3-67 is an exception; it contains lower am- 
phibolite-facies hornblende-biotite-plagioclase 
gneiss. Similar amphibolite-facies rocks are found 
south of the inferred Pender fault in two wells. 

East of a line passing from central Bertie County 
through eastern Pitt County to western Jones 
County, basement consists of wide bands of low 
magnetic relief interpreted as metamorphosed sedi- 
mentary rocks and felsic volcanics interspersed 
with narrow bands of north-south trending, highly 
magnetic rocks that are probably mafic 



11 



metavolcanic rocks. Metasiltstone is found in PT- 
T-l-85 and a silty metamudstone occurs in BT-T- 
1-73. Hertford County oil test HT-OT-1-49 con- 
tains a calcareous biotite phyllite and represents 
the highest grade rocks in this region. 

Few of the magnetic highs inferred to represent 
metavolcanic rocks in this belt have been drilled, 
although a felsic (rhyolite or dacite) phyllitic crys- 
tal tuff is found in CM-OT-1-65 and CM-OT-1-53. 
Samples examined in this study were chips, but 
Denison and others ( 1 967) reported eutaxitic struc- 
ture and relict pumice fragments in a core from 
CM-OT-1-65. They determined a Rb-Sr model 
age on this rock of 408+40 Ma (see Table 2 for 
comparison to other rock ages). A metamorphosed 
intermediate volcanic rock which seems to be an 
andesite crystal tuff is found in oil test GA-OT-1- 
7 1 in eastern Gates County. To the south, ON-OT- 
1-60 penetrated felsic metavolcanic rock. Relict 
plagioclase phenocrysts (An^) in a fine-grained 
slaty groundmass suggest an approximate compo- 
sition of metadacite in Onslow County oil test ON- 
OT-2-59. 

Three intense magnetic highs occur in the Eliza- 
beth City area. This signature resembles those 
produced by gabbros exposed in the Piedmont. A 
relatively large (18 km diameter, 260 square km) 
felsic pluton in Gates County test hole VPI- 1 was 
named the "Dort Granite" by Becker (1981). This 
pluton consists of mildly deformed granodiorite 
and is mapped based on a localized, equant gravity 
low. Much of the indicated area of the Dort pluton 
is within a positive magnetic anomaly, so part of 
the pluton may be magnetic or may be covered by 
mafic metavolcanic rocks. 

Two northwest- southeast trending, narrow, 
positive magnetic anomalies, suggestive of Juras- 
sic diabase dikes, occur within the area underlain 
by the Rocky Mount granitic pluton. In the remain- 
der of the region east of the Hollister fault, mag- 
netic anomalies attributable to diabase dikes are 
rare to absent. Either the Coastal Plain cover is too 



thick to allow definition of any other such anoma- 
lies; or, alternatively, the anomalies due to 
metavolcanic rocks may be so intense and compli- 
cated that the small anomalies due to dikes are 
obscured. 

Hatteras Belt 

This belt, as named by Daniels and Zietz (1978) 
stretches from Norfolk, Virginia, southward to 
Onslow County and is present in the offshore shelf 
basement along the entire coast to south of 
Wilmington. Two large batholiths comprise much 
of this region; the remainder of the rocks are schist 
and gneiss. The Hatteras terrane defined by Horton 
and others (1989) is essentially identical with the 
Hatteras belt described by Daniels and Zietz ( 1 978) 
and Daniels and Leo (1985); the rocks included are 
the amphibolite facies metamorphic rocks and the 
batholiths. 

The Cape Hatteras batholith (informally named 
by Lefort (1989, p. 74) — the name was not 
previously used by Scott and Cole (1975) as Lefort 
implies) underlies an area of about 1 1,500 square 
km from southern Virginia to just south of Cape 
Hatteras. This large batholith has been noted 
previously by Denison and others (1967), Daniels 
and Zietz (1978), and Watkins and others (1985) 
based on drilling records and the large negative 
(-40 milligals) gravity anomaly. Watkins and 
others (1985) termed the anomaly the Albermarle 
Sound Gravity Anomaly and modeled the anomaly 
with a granite pluton 10 km thick. It is important to 
note that the Cape Hatteras batholith shown in this 
report is indicated on the maps by Daniels and Leo 
(1985) and Thomas and others (1989) as a smaller 
batholith or several disconnected plutons. 

There are no data avilable to resolve the ques- 
tion of which interpretation of the subcrop is cor- 
rect. DR-OT-1-71 penetrated an almandine+ 
cordierite+biotite granite which was named the 
Stumpy Point granite by Russell and others (1981) 
and Speer (1981). DR-OT-2-73 contains what 



12 



Table 2. Reported isotopic ages of eastern Piedmont and Coastal Plain plutons and of eastern Piedmont 
metamorphism. Dates from early publications have not been recalculated. For other dates in North 
Carolina see McSween and others (1991). 



Pluton 


Age (Ma) 


Method 


Reference 


Plutons in the Eastern Piedmont 








Lemon Springs granite 


430±13 


Rb-Sr whole rock 


Campbell and Kish, 1989 


Lillington granite 


297+4 


Rb-Sr whole rock 


Kish, 1983 


Sims granite 


287±9 


Rb-Sr whole rock 


Wedemeyer and Spruill, 1980 


Castalia granite 


314+11 


Rb-Sr whole rock 


Fullagar and Butler, 1979 


Rocky Mount pluton 


345±1 


Rb-Sr whole rock 


Fullagar and Spruill, 1989 


Butterwood Creek granite 


292+30 


Rb-Sr whole rock 


Russell, Russell, and Farrar, 1985 


Medoc Mountain granite 


301±6 


Rb-Sr whole rock 


Fullagar and Butler, 1979 


Plutons in the Coastal Plain subsurface 








Fountain granite (outcrop) 


531+60 


Rb-Sr whole rock 


Mauger and others, 1983 


Portsmouth, Virginia 


263±25 


Rb-Sr whole rock 


Russell, Speer, and Russell, 1985 


Socony Mobil #1 (DR-OT-1-65) 


585±40 


Rb-Sr whole rock 


Denison and others, 1967 


Socony Mobil #1 (DR-OT-1-65) 


520±30 


Rb-Sr muscovite 


Denison and others, 1967 


Socony Mobil #2 (DR-OT-2-65) 


354+7 


K-Ar biotite 


Denison and others, 1967 


Socony Mobil #3 (HY-OT-1-65) 


610±60 


Rb-Sr whole rock 


Denison and others, 1967 


Stumpy Point granite (DR-OT-1-71) 


583+46 


Rb-Sr whole rock 


Russell and others, 1981 


Camp Lejeune qtz. monzonite (ON-T-1 


-79) 630±39 


Rb-Sr whole rock 


Russell and others, 1981 


Metamorphic Dates in the Piedmont 








Raleigh Gneiss 


246, 241 


Rb-Sr whole rock 


Russell, Russell, and Farrar, 1985 


Falls Leucogneiss 


238, 242 


Rb-Sr whole rock 


Russell, Russell, and Farrar, 1 985 


Lumberton area (VPI-2) 


314+22 


Rb-Sr whole rock 


Russell and Russell, 1980 


Lumberton area (VPI-2) 


241,247 


Rb-Sr bio-wh rock 


Russell and Russell, 1980 


Camp Lejeune qtz. monzonite (ON-T-1 


-79) 340,371 


Rb-Sr bio-wh rock 


Russell and Russell, 1980 



seems to be a sheared two-mica granite. DR-OT- 
1-73 contains an alkali feldspar granite. Other- 
wise, the common rocks are normal granites and 
aplites, with the exception of an altered diorite in 
DR-OT-4-65 and altered biotitic diabase in DR- 
OT-2-65 (as first reported by Denison and others 
(1967) and listed by Daniels and Leo (1985) as a 
lamprophyre). Most of the batholith area is mag- 
netically flat, except for two large (800 gamma) 
magnetic highs, one on the west side of the batholith 
and one at the south end, which are both inferred to 
reflect mafic plutons. 

Many of the samples in the Cape Hatteras 
batholith are slightly strained and altered. Samples 



from oil test wells DR-OT-1-65 and DR-OT-2-74 
exhibit mortar texture, strained quartz, and bent 
plagioclase grains. Denison and others (1967) 
reported a Rb-Sr whole rock model age of 585+40 
Ma for basement in DR-OT-1-65, a 520±30 mus- 
covite age, and a 455+40 isochron age (interpreted 
as the shearing age); Russell, and others (1981) 
reported a Rb/Sr age of 583+46 Ma for their Stumpy 
Point granite (DR-OT-1-71). 

A composite gabbro-diorite-quartz monzonite- 
granite batholith, here informally named the Carteret 
batholith, underlies approximately 7,000 square 
km of Carteret, Craven, Pamlico, Jones, and part of 
Onslow counties. This batholith is distinguished 



13 



from the Cape Hatteras batholith by a different 
geophysical expression. Several small gravity 
anomalies underlie the region (25 milligal low in 
the western part, 15 milligal highs in the eastern 
part), and the magnetic field consists of a number 
of 300 gamma highs and 200 gamma lows, all 
about 1 3 km across. Since this batholith is partially 
of intermediate composition, its average density 
may be similar to densities of the wall rocks and 
thus it does not have a broad large negative gravity 
anomaly as does the Cape Hatteras batholith. Al- 
ternatively, Thomas and others (1989) point out 
that the batholith may be much thinner than the 
Cape Hatteras batholith. Daniels and Leo (1985) 
map this area as a region of small plutons and 
metamorphic rocks. 

The western half of the Carteret batholith con- 
sists mostly of quartz monzonite, hornblende quartz 
monzonite (ON-T-1-79 — Russell and others, 
1981), granodiorite (ON-OT-4-66), and smaller 
bodies of diorite and gabbro interpreted from local- 
ized magnetic highs. 

In the eastern half of the batholith, two oil test 
wells in southern Carteret County (CR-OT-2-61 
and CR-OT-3-61) penetrate granite. However, in 
northern Carteret and southern Pamlico counties, a 
region of slightly higher magnetic values and higher 
Bouguer gravity values consists of quartz monzo- 
nite (PA-OT-1-47), granodiorite (CR-OT-5-46), 
and diorite (CR-OT-4-46). Thispartof the Carteret 
batholith is more sheared and altered than the rest. 
The Camp Lejeune quartz monzonite in ON-OT- 1 - 
79 has been dated as 630±39 Ma (Rb-Sr) by Russell 
and others (1981). Local, equant, intense magnetic 
highs in the schist and batholith belt are probably 
produced by gabbroic plutons, although no well 
data are available to test this. 

Immediately to the west of these large plutonic 
bodies lies a discontinuous belt of schist and gneiss 
ranging from 5 to 50 km wide, including biotite 
zone rocks of the greenschist facies and an approxi- 
mately 5-km-wide band of amphibolite fades schist 



and gneiss. Rocks in the biotite zone are found in 
Tyrell County oil tests TY-OT- 1 -7 1 and TY-OT-2- 
7 1 . In one hole in Currituck County, CK-OT- 1-65, 
toward the north end of the belt, garnet and an- 
dalusite were reported by Denison and others (1967) 
and staurolite was reported by Daniels and Leo 
(1985). Westof the Carteret batholith, biotite schists 
are found in DP-T-2-82 and in ON-OT- 1-50; horn- 
blende-biotite gneiss is found in ON-OT-3-67. 
Most of the metamorphosed rocks apparently have 
sedimentary protoliths, probably mudstones and 
sandstones. South of the inferred Pender fault zone 
two wells, PE-OT-2-66 and PE-OT-4-66, pen- 
etrate amphibolite facies rocks. Whether these 
areas should be included as part of the Hatteras 
terrane, as in Horton and others (1989), is unclear. 

As defined by Horton and others (1989), the 
Hatteras terrane would only include the amphibo- 
lite-facies rocks and the batholiths. However, 
metavolcanic rocks in CR-OT-2-73 within the 
Carteret batholith and near the coast are greenschist- 
grade metatuffs; and amphibolite-facies rocks in 
ON-OT-3-67 are farther west than lower grade 
rocks in ON-OT- 1-67. Thus, the Hatteras terrane 
is better termed a belt, or the biotite zone rocks of 
upper greenschist facies will have to be included to 
allow a western boundary to be defined. Indeed, 
terrane boundaries are normally drawn at major 
faults rather than at zones of high metamorphic 
gradient; so the Hatteras belt should presently be 
included in the Roanoke Rapids terrane. 

The majority of the plutonic rocks in this belt 
yield Rb-Sr isotopic ages in the range of 630 to 580 
Ma, latest Precambrian or earliest Cambrian (Table 
2). Scattered Ordovician, Devonian, and Missis- 
sippian K-Ar and Rb-Sr isotopic ages suggest 
shearing and plutonism in middle to late Paleozoic. 
The granodiorite to biotite tonalite pluton in Suf- 
folk, Virginia, at the northern end of this belt yields 
a Rb-Sr isochron age of 262+25 Ma, interpreted 
(by the authors) as an igneous age of crystallization 
(Russell and others, 1981; Russell and others, 
1985). Andalusite-garnet-two-mica schist in CK- 



14 



OT- 1 -65 yielded a 253±5 K- Ar biotite age (Denison 
and others, 1967) which is similar to the cooling 
and uplift ages in the easternmost Piedmont (Mauger 
and others, 1987). 

METAMORPHISM 

Basement rocks beneath the North Carolina 
Coastal Plain exhibit metamorphic effects ranging 
from slight hydrothermal alteration to chlorite- or 
white-mica-bearing slates to amphibolite-grade 
gneisses and schists. Metamorphic grade in out- 
cropping Piedmont rocks along the western edge of 
the Coastal Plain has been described by Farrar 
(1985a), Kite and Stoddard (1984), Campbell 
(1984), Horton and Stoddard (1986), Boltin and 
Stoddard (1987), the Geologic Map of North Caro- 
lina (North Carolina Geological Survey, 1985), 
and Butler (1991). 

With the exception of two regions in Richmond 
County (one due to contact metamorphism around 
the Lilesville pluton) and Johnston County (where 
the Wake- Warren antiform lies), the chlorite zone 
of regional metamorphism is present in the Pied- 
mont at the Coastal Plain edge (Butler, 1991). 
Beneath the west and northwestern Coastal Plain, 
four isolated regions of biotite-bearing schistose 
rocks are found (Figure 1). One is in Moore 
County, west of the Nutbush Creek fault. One lies 
in Edgecombe County, where the outcrops at Foun- 
tain (Mauger and others, 1983) and nearby wells 
are lower-amphibolite-facies metagranite, schist, 
and gneiss — probably in the core of an 
anticlinorium. A third lies in Robeson County, 
where Becker (1980) and Pratt and others (1985) 
report lower amphibolite-f acies metavolcanic rocks 
above a roofed granitic pluton. The fourth is a 
small area in Hertford County, where one well 
penetrated biotitic metasandstone. 

The largest area of schist and gneiss is associ- 
ated with the batholiths that lie along the coast. 
Biotite- and garnet-bearing rocks lie along the west 
side of the Cape Hatteras batholith, and a wider 



area of biotite-muscovite-bearing schists lie west 
of the Carteret batholith (Daniels and Leo, 1985; 
Horton and others, 1989). At least part of the 
schists bordering the coastal batholiths are prob- 
ably in lower amphibolite facies (Denison and 
others, 1967), but it is unclear how extensive an 
area is thus affected. One isolated area of lower 
amphibolite facies (BW-T-1-79) has been retro- 
graded heavily to greenschist facies. Since this 
coastal zone of batholiths and schists has a higher 
metamorphic grade and far more plutonic rocks 
than either the Carolina slate belt or the Eastern 
slate belt, this region is readily differentiated from 
the remainder of North Carolina Coastal Plain 
basement rocks. 

The age of the metamorphism is still not estab- 
lished, but a K-Ar age of 253+5 Ma determined for 
a muscovite in the belt (Denison and others, 1967) 
implies Alleghanian cooling and would make a 
Taconic or Alleghanian metamorphism possible. 
The origin of this distribution of metamorphic 
grades is unclear. Some of the increased regional 
metamorphic grade may be due to the intrusion of 
syntectonic plutons in the Lumberton area and in 
the coastal batholithic belt. In other cases, such as 
in the Pitt County area around Fountain, the expo- 
sure of lower amphibolite facies may be due to 
uplift and erosion in the core of a large anticline. 

STRUCTURE 

Trends of units based on the magnetic map 
indicate a dominant fold event with north-south- 
trending axial surfaces beneath the Coastal Plain. 
A subordinate trend is evident through the southern 
and southwestern Coastal Plain, where units and 
folds trend northeast-southwest to east- west. The 
only practical way to determine whether a fold is an 
anticline or syncline would be to assume that the 
plunge directions are consistent with those ob- 
served in the Piedmont. This assumption, how- 
ever, does not appear warranted from the sparse 
available data. The only drill hole for which the 
structural dip direction is known is the Lumberton 



15 



well (VPI-2, see seismic data in Pratt and others, 
1985) but the magnetic trends in the area are not 
clear enough to convert the approximately 20- 
degree southeast dip into regional- scale folds. 
Thus, no fold closures on the map have been 
labeled with anticline or syncline symbols. 

Plate 1 identifies five major faults that have 
been inferred to underlie the Coastal Plain. The 
westernmost in the region is the Nutbush Creek 
fault. This structure was originally described by 
Casadevall (1977) and extended by Hatcher and 
others (1977) and by Farrar (1985a, 1985b). It 
crops out in the Piedmont west of Raleigh. This 
fault extends south and southwest under the North 
Carolina Coastal Plain into South Carolina where 
it may connect with the Modoc fault of Hatcher and 
others (1977). This fault has dextral offset as 
indicated by Farrar (1985a), Horton and others 
(1986), and Druhan and others (1988) who esti- 
mated 160 km of dextral offset between 312 and 
285 Ma based on the ages of unsheared and sheared 
granite plutons dated by whole-rock Rb/Sr. 

Near Raleigh, the Nutbush Creek fault is marked 
by a prominent, narrow, north-trending positive 
magnetic anomaly (Stoddard and others, 1991); 
but as the fault passes under the Coastal Plain it can 
only be inferred on the basis of apparent trunca- 
tions of magnetic anomalies. Near the South Caro- 
lina border it is inferred to pass between a parallel 
positive anomaly on the west and a broad magnetic 
low on the east. 

The Hollistermylonite zone, previously mapped 
by Kite and Stoddard (1984), Boltin and Stoddard 
(1985), and Farrar (1985a) and inferred earlier on 
the basis of regional magnetics by Hatcher and 
others (1977), is due to a major dextral strike-slip 
fault zone which trends north-south through 
Hollister (Halifax County) and continues south- 
ward on a line west of Rocky Mount, Wilson, and 
Goldsboro (Horton and others, 1989, 1991; Sacks 
and others, 1991). Where the zone crops out, there 
are clear textural indicators of dextral motion 



(Farrar, 1985a). Apparent drag of units and aero- 
magnetic anomalies truncated by the zone indicate 
dextral offset. Smits and others (1988) pointed out 
that later phases of the Butterwood Creek pluton 
are not mylonitized, though earlier phases are 
mylonitized. 

Russell, Russel, and Farrar (1985) present Rb/ 
Sr dates of 251 Ma for the sheared pluton, and 
292+30 Ma for the unfoliated pluton away from the 
fault, giving a bracket for the age of dextral fault- 
ing. Hatcher (1990) suggested a possible offset 
across the Hollister fault based on the correlation of 
possible early fold axial surfaces. If the correlation 
is correct, approximately 25 km of dextral offset is 
indicated. This may be compared to the offset 
indicated by the parts of the Butterwood Creek 
pluton, which show about 8 km of dextral offset 
(Farrar, 1985a). Recently, Vyhnal and McSween 
(1990) showed that the aluminum barometer in 
hornblende from granitic plutons east and west of 
the fault indicated between 4 and 15 kilometers of 
relative uplift of the west side of the fault, displace- 
ment that they concluded took place earlier than the 
Alleghanian dextral displacement. The metamor- 
phosed tuff in NA-A-1-84, located adjacent to the 
fault, is a protomylonite. 

Of the two sub-Coastal Plain inferred branches 
of the Hollister fault that are shown on Plate 1, the 
southwest-trending one is similar to, but differs 
slightly in position, from the one shown by Hatcher 
and others (1977) and Hatcher (1990). 

The southward-extending branch of the 
Hollister fault zone shown on Plate 1 is similar to 
the version shown by Horton and others (1991). It 
divides crust of lower regional magnetic values on 
the west from the higher values on the east, and a 
long prominent northeast-trending anomaly on the 
east side is truncated by the extension shown. This 
south-trending branch of the Hollister is shown 
truncated by the inferred Pender fault which di- 
vides north-south-trending anomalies north of the 
fault from east- west- trending anomalies to the south. 



16 



The inferred southwest-curving branch of the 
Hollister fault forms the east boundary of the large 
area of metamudstone and metasandstone in 
Sampson, Cumberland, and Hoke counties and the 
volcanic rocks of the Lumberton area in Robeson 
County. The southwest 50 km of this inferred fault 
is poorly constrained, since no clear magnetic 
lineament is present. 

A pattern of truncated magnetic anomalies 
suggests a second fault, indicated on Plate 1 as the 
inferred Roanoke Island-Goldsboro fault, that 
passes east-west to southwest under Roanoke Is- 
land, Greenville, Farmville, and Goldsboro. This 
structure is totally concealed by Coastal Plain 
cover. Some possible offsets suggest a dextral 
displacement. Although the east end of this in- 
ferred fault becomes difficult to follow as it passes 
into the coastal batholith belt, it seems to project 
through Roanoke Island on trend with a high- 
angle, south-wall-down-thrown fault mapped by 
Almy (1987) on the basis of two seismic lines. The 
seismic data indicate that the fault near Roanoke 
Island cuts the basement surface as well as the 
lower part of the Cretaceous section. It could 
represent later reactivation of an earlier basement 
fault. 

The southern extension of the Hollister fault 
and several other north-south trends are truncated 
by an east-west discontinuity across southern 
Robeson, Pender, and Bladen counties, herein 
termed the Pender fault. This trend has previously 
been described by Higgins and Zietz (1983) as the 
Carolina-Mississippi fault. They placed the dis- 
continuity farther south than on the present map 
and interpreted it as a dextral fault zone, based 
merely on their inability to correlate across the 
lineament in South Carolina and Georgia. If the 
discontinuity is a fault, it would probably merge 
with the northeast-trending Piedmont fault system 
in South Carolina described by Hatcher and others 
(1977). 

In the region just east of Greenville, where 



Daniels and Zietz (1978) inferred a Triassic basin, 
lies a boundary between common positive linear 
magnetic anomalies on the west (interpreted to be 
due to metavolcanic rocks) and an area of low 
magnetic relief on the east containing phyllitic 
metasedimentary rocks (Sampair, 1979). On Plate 
1 , a fault is inferred on this boundary, based on the 
truncation of a magnetic anomaly in Duplin County 
(see also lineament shown by Daniels and Leo 
(1985) in the same location). Since this inferred 
fault parallels many of the strikes of the units in the 
area, it may represent an east-dipping thrust, simi- 
lar to many detected by Pratt and others (1988) on 
the 1-64 seismic line across the southeast Virginia 
Coastal Plain. Considering how common south- 
east-dipping faults are in the Coastal Plain base- 
ment of Virginia, many of the north-trending con- 
tacts in the North Carolina Coastal Plain basement 
are probably east-dipping thrusts as well. 

TECTONIC IMPLICATIONS 

Kite and Stoddard (1984) referred to the possi- 
bility that there might be extensive oceanic crust 
beneath the Coastal Plain. However, other than 
local linear gravity and magnetic highs, the Coastal 
Plain does not exhibit high gravity values and the 
rocks are only slightly more magnetic than the 
main slate belt rocks. Schneitzler and Allenby 
(1983) proposed that the relatively higher mag- 
netic values under the Coastal Plain might be 
explained by a more magnetic lower crust (lower- 
most 13 km). Pratt and others (1988) utilized 
seismic data to constrain gravity models, and con- 
cluded that the lowermost 8-10 km of the south- 
eastern Virginia crust had a density of 3.0 Mg/m 3 . 

Seismic refraction studies by James and others 
(1968), Lewis and Meyer ( 1 977) , and gravity mod- 
eling by Hutchinson and others (1982) have shown 
that the continental crust is 38 km thick near Cape 
Fear and 40 km thick under Pamlico Sound. Pratt 
and others (1988) interpreted a seismic line in 
southeast Virginia to indicate that the crust was up 
to 40 km thick near the coast. Crustal velocities are 



17 



6 km/sec in the shallow crust and 6.7 to 7.0 km/sec 
in the deep crust (Warren, 1968). The free-air 
gravity anomaly is adequately modeled using the 
refraction data and assuming that the upper 15 km 
of crust has a density of 2.7 gm/cc and that the 
lower crust has a density of 3.0 gm/cc (Hutchinson 
and others, 1982). This model describes continen- 
tal crust consisting of an upper layer of granitic 
plutons, metamorphosed sedimentary rocks, and 
felsic to mafic metavolcanic rocks, and a lower 
crust of gabbroic rocks in isostatic equilibrium. 

Drilling to date has not encountered any ultra- 
mafic rocks beneath the North Carolina Coastal 
Plain. If any oceanic crust and upper mantle rocks 
are present, they likely are in a narrow zone rather 
than widely distributed (see Figure 10 in Pratt and 
others (1988) who modeled a gravity high east of 
Richmond, Virginia, with a thin, steeply east-dip- 
ping slab of 2.87 Mg/m 3 density rocks). Since 
serpentinite is not dense and a suture may be 
marked by an oceanic- sediment accretion complex 
with only minor interleaved volcanic rocks, a thin 
zone of these rocks might be present and not show 
up in either the magnetic or gravity fields. Thus, 
although most of the Coastal Plain basement con- 
sists of continental crust or mature island-arc ma- 
terial, sutures marked by mantle and oceanic mate- 
rial have not been identified beneath the North 
Carolina Coastal Plain and, if present, are well 
hidden. 

The central and southern Appalachian area has 
been divided into proposed tectonostratigraphic 
terranes by Horton and others (1989) and Horton 
and others ( 1 99 1 ) — a more detailed treatment than 
the terrane scheme of Williams and Hatcher (1982). 
The named terranes represent fault-bounded blocks 
interpreted to have internally homogeneous stratig- 
raphy and geologic histories that are different from 
those of contiguous terranes. Presently, there is not 
enough stratigraphic evidence, radiometric dates, 
or structural data to confirm the validity of terranes 
proposed for the eastern North Carolina Piedmont 
and Coastal Plain basement. Thus, we tentatively 



follow the nomenclature of Horton and others 
(1989) and the references therein (see description 
of terranes above in Geologic Map and Description 
of Lithologic Belts section). 

The plate tectonic significance of the terranes 
and their boundaries is still unclear. There are 
small ultramafic masses west of the Nutbush Creek 
mylonite zone (Horton and others, 1986), indicat- 
ing that there may be a suture near the strike-slip 
fault. However, the Carolina and Spring Hope 
terranes may just be segmented parts of the same 
island arc (Horton and others, 1989) since the suite 
of rocks in the Carolina terrane is similar to that in 
the Spring Hope terrane (Figure 1 and Plate 1). But 
Fullagar and others (1987) have pointed out that a 
Devonian (Rb-Sr whole-rock dates of 365 and 386 
Ma) regional metamorphic event may have af- 
fected the Spring Hope terrane and not rocks in 
nearby parts of the Carolina terrane, thus suggest- 
ing different metamorphic histories. Also, the 
Bouguer gravity anomaly of the Carolina terrane 
(Black, 1986) is much more positive than that of 
the Spring Hope, indicating a denser (or thinner) 
crust. 

In the Roanoke Rapids terrane, the Halifax 
County complex, a mafic-ultramafic complex in- 
terpreted as an ophiolite lies on the east side of the 
Hollister fault zone, suggesting another possible 
suture (Kite and Stoddard, 1984). The Hollister 
fault zone is a late Paleozoic feature (Farrar, 1985a; 
Russell, Russell, and Farrar, 1985; Dallmeyer, 
1991), and must be superimposed on the earlier 
possible suture. The stratigraphy, metamorphic 
grade, and structure are too poorly known to deter- 
mine if they are similar to those of the Spring Hope 
and Carolina terranes. Unlike the fault boundary 
on the west side, the south and east boundaries of 
the Roanoke Rapids terrane are poorly fixed. Horton 
and others (1989) emphasized that "the northwest- 
ern boundary of the Charleston terrane is poorly 
constrained and subject to speculation," and they 
"tentatively portrayed ...(it)... as a modified ver- 
sion of the magnetic lineament which Higgins and 



18 



Zietz (1983) refer to as the Carolina-Mississippi 
fault." In light of this study, it would seem best to 
shift the boundary between the Roanoke Rapids 
terrane and the Charleston terrane to the hypoth- 
esized Pender fault zone. 

The Hatteras terrane boundary was fixed by 
Horton and others (1989) as the edge of amphibo- 
lite facies schists and gneisses and Late Protero- 
zoic plutons in the coastal belt. If the terrane 
boundary is retained, it will have to be moved 
inland slightly from where Horton and others (1989) 
placed it so as to coincide with the larger area of 
plutonic rocks mapped in the present study. A 
somewhat different terrane correlation is suggested 
by Secor and others (1990), who conclude that the 
Hatteras terrane has much in common with the 
Tallahasee-Suwanee terrane of subsurface Ala- 
bama, Florida, and southern Georgia. Along with 
Watkins and others (1985), Secor and others (1990) 
suggest that the batholithic area along the coast of 
North Carolina is a fragment of west Africa. 
Dallmeyer (1989, 1991) and McSween and others 
( 1 99 1 ) indicate the possibility that the North Caro- 
lina Coastal Plain basement may be a fragment of 
Gondwana continental crust (Pan African orogen). 

The Hatteras terrane does appear to be a frag- 
ment, since the batholith belt does not seem to 
extend far to the north or south, and thus continu- 
ations of it may indeed be in the Pan African belt, 
where events circa 550 Ma are apparently of the 
same age as in the Hatteras belt (Dallmeyer, 1989). 
Since no fault boundary can presently be drawn 
between the Hatteras terrane and the Roanoke 
Rapids terrane, it is unclear how much of the 
basement beneath the North Carolina Coastal Plain 
could be included as a fragment of Gondwana. 

A somewhat different, and rather detailed tec- 
tonic analysis of this region was made by Lefort 
(1989), who placed the eastern half of the Roanoke 
Rapids terrane, most of the Hatteras terrane, and 
the Charleston terrane in his "Senegal plate" along 
with an area in west Africa including the country of 



Senegal. He indicated a major suture extending 
east-west across the North Carolina continental 
shelf, through the Albemarle Sound area, and then 
arcing toward the northwest near Richmond, 
Virgina. 

On the north side of this suture, in northern 
North Carolina and in the Coastal Plains of Vir- 
ginia and Maryland, he postulates a basement gen- 
erally older than 1000 Ma, with tectonic trends not 
characteristic of the Appalachians and correlative 
with similar age rocks of the Reguibat Uplift of 
west Africa. The "Chesapeake Bay Suture" that he 
places through Albemarle Sound would pass di- 
rectly through the northern end of the gravity low 
caused by the Cape Hatteras batholith, rather than 
truncating it as suggested by his map. Also, broad 
north-trending magnetic lows and highs indicative 
of metasedimentary and metavolcanic rocks are 
not obviously truncated by the proposed suture. 
The trends of magnetic anomalies, and the charac- 
ter of the anomalies north and south of the suture 
are not very different. No isotopic ages are avail- 
able in eastern Virginia to suggest presence of 1 000 
Ma basement, and the structures on the 1-64 seis- 
mic line (Pratt and others, 1988) are consistent with 
Appalachian structures. Although correlations with 
some west African rocks could be correct, the 
Chesapeake Bay suture path through North Caro- 
lina seems poorly supported. 

The only presently available limits on terrane 
docking times appear to be brackets between the 
Taconic docking time for the Carolina terrane 
(Vick and others, 1987) and the Carboniferous 
orogeny and collision with Africa (Russell, Russell 
and Farrar, 1985). Vick and others (1987) noted 
that the 450 Ma age of deformation and metamor- 
phism in the North Carolina slate belt apparently 
coincides with the docking age of the slate belt as 
determined by paleomagnetic data analysis. Inter- 
estingly, Denison and others (1967) reported a 
"shearing age" of a coastal granite in DR-OT-1-65 
of 455 Ma (Rb-Sr isotopic age). Thus, there is 
some suggestion that the Late Ordovician orogeny 



19 



was present across the slate belt and the Coastal 
Plain basement and that the Hatteras terrane also 
arrived in the Ordovician. 

Horton and others (1989) suggest that the Caro- 
lina terrane arrived in the Ordovician, but that the 
more outboard terranes could have arrived anytime 
between the Ordovician and Carboniferous. If the 
hypothesis by Secor and others (1990) is correct, 
the western half of the Coastal Plain basement 
arrived with the Carolina terrane ( Avalonian rocks) 
and the coastal batholithic area (Hatteras terrane) 
arrived as part of the African plate in the Carbon- 
iferous, at approximately 300 Ma. 

In terms of our understanding of Mesozoic 
tectonics, this study adds the constraint that there is 
only a small volume of Triassic or Jurassic sedi- 
mentary rocks in basins under the Coastal Plain. 
As pointed out by deBoer and others (1988), the 
northeastern trend of the bounding normal faults of 
the basins indicates northwest-southeast exten- 
sion, but strike-slip motion on cross-faults is prob- 
able. Also, the Jurassic dikes were probably in- 
truded at the peak of extensional activity. Their 
varying orientation from northwest trends in Geor- 
gia to north and northwest in North Carolina to 
northeast in New England have led deBoer and 
others (1988) to speculate that this is a "gash vein" 
orientation caused by clockwise rotation of Africa. 

CONCLUSIONS 

The variety of rock types, styles of deforma- 
tion, and metamorphism of the Coastal Plain base- 
ment appear similar to those of the adjacent Eastern 
slate belt and Raleigh belt. However, two east- 
west-trending faults are present within this area. 
The volume of late Precambrian plutonism in the 
Hatteras terrane is far greater than in the exposed 
slate belt. The location of the Hollister fault is 
uncertain south of Goldsboro but may be inter- 
rupted in western Pender County by the inferred 
Pender fault. Except for the covered portions of the 
Wadesboro, Sanford, and Ellerbe basins and the 



possible edge of a basin beneath Cape Hatteras 
(Klitgord and others, 1988; Benson, 1984), no 
early Mesozoic rift basins have been confirmed by 
drilling. The only sizeable buried Triassic basins 
are apparendy offshore (Hutchinson and others, 
1982). Proposed sutures and terrane boundaries 
should take into account both the large batholiths 
and the proposed Pender fault zone. 

ACKNOWLEDGEMENTS 

The authors wish to acknowledge the fol- 
lowing individuals who provided technical review 
of and comments on the various manuscript ver- 
sions of this publication: J. Wright Horton, Jr., J. 
Alex Speer, J. Robert Buder, Carl E. Merschat, P. 
Albert Carpenter, HI, Jeffrey C. Reid, and Charles 
H. Gardner. Billie J. Flynt, Jr. provided able 
cartographic assistance and Stephen T. Reid pro- 
vided editorial review. The senior author thanks 
Richard Spruill for suggesting the project and the 
ECU Research/Creative Activities Committee for 
a grant which supported part of the research. 

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22 



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23 



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24 



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30 



APPENDIX B - Thin Section Descriptions 



Introduction 

The following descriptions include all petto- 
graphic descriptions made as part of this study plus 
numerous descriptions compiled from the litera- 
ture. Appendix C, which follows this section, 
includes photomicrographs of many of the thin 
sections described below. Those thin sections for 
which photomicrographs are included in Appendix 
C are indicated by an asterisk (*). 

Thirteen whole petrographic slides were made 
from drill cores. All other sections were made from 
grain mounts of chips mostly in the size range of 1 
to 5 mm. Little textural evidence is preserved for 
coarse grained rocks, since the chips are the same 
size, or smaller than, the grain size of the rock. 
Mineralogical percentages, and thus the igneous 
rock type, can only be approximately determined. 
Igneous rock type names follow the I.U.G.S. clas- 
sification of Streckeisen (1976). The compositions 
and classification of finer grained volcanic and 
sedimentary rocks are better determined, since 
some textures and mineral percentages can be fully 
described. 

Descriptions 

BF-OT-1-63 * One chip of possible fine-grained 
metasandstone consisting of quartz (.12 mm), and 
white mica (.01 mm), with a single grain of fine 
magnetite. Grains of quartz are slightly strained 
with some grain boundary suturing. No layering is 
present, but there is a very slight slaty foliation. 
BF-OT-4-63 * Chips of quartz- sericite slate - most 
probably metasiltstone, but some material looks as 
if it could bemetavolcanic. Consists of sericite (.01 
mm), quartz (.08 mm), and magnetite (.06 mm) 
with good to poor schistosity. 
BL-OT-1-59 * Full thin section from core of 
metabasalt with a few relict microphenocrysts of 
albitized plagioclase. Consists of biotite (.15-.30 



mm), white mica (.03 mm), epidote (.15 mm), 
chlorite (.06 mm), plagioclase (.4-.9 mm), and 
quartz (.06 mm) in veins with minor titanite, 
leucoxene, and magnetite. Although the biotite is 
coarser than in many rocks, there is not a good 
foliation. One epidote vein has been folded. 
BL-T-1-81 * Sericite phyllite chips which ex- 
hibit good schistosity. Consists of 90 percent 
sericite (.06 mm), 3 percent quartz (.01 -.06 mm), 
and 7 percent magnetite (.03-. 06 mm) with minor 
calcite. 

BL-T-2-84 * Chips of metasiltstone with poor 
cleavage. Ninety percent of the rock is quartz (.03 
-.12 mm). White mica (.01 mm), and opaques (.06 
mm), and other minerals comprise 10 percent. 
BL-T-1-88 Chips of hematite- sericite phyllite 
and chloritic quartzite. Phyllite consists of white 
mica (.05 mm), hematite (.03 mm), chlorite, and 
minor quartz. Quartzite has only quartz (. 1 -.9 mm) 
and chlorite (.06 mm). 

BT-T-1-73 * Full thin section of a metamudstone 
with slaty cleavage - probably of volcaniclastic 
origin. Consists primarily of quartz silt grains (.05- 
. 1 1 mm), white mica (.08 mm), minor chlorite, and 
carbonate in thin folded veins. Minor opaques are 
mostly magnetite with less pyrite. Two separate 
orientations of white mica give the rock two poorly 
developed S surfaces. 

BT-T-1-82 * Full thin section of unfoliated 
metavolcanic rock - an intermediate crystal- 
(lapilli?) tuff. Epidote (. 1 -. 1 5 mm) is common and 
plagioclase (1.1 mm), although albitized, shows an 
idiomorphic relict volcanic texture. The carbonate 
(.15 mm), white mica (.04 mm), quartz (.06 mm), 
and chlorite (.05 mm) are metamorphic. There is 
also very minor magnetite and rutile. 
BW-OT-1-71 * Chips of weakly phyllitic quartz- 
sericite rock - possibly an altered meta-tuff (pos- 
sible ghosts of lapilli). Quartz (.01-.03 mm), white 
mica (.02 mm), and fine-grained rutile, magnetite, 
and pyrite are only recognizable minerals. 
BW-T-1-73 * Probably quartzite, but could be 



31 



strained aplite chips. Consists of quartz (.15 mm), 
microcline (. 15 mm), green-brown biotite (.2 mm), 
and minor albite (. 1 mm). No schistosity is present. 
BW-T-1-79 Described by Daniels and Leo 
(1985) and Farrar (1980a) as an intermediate to 
mafic gneiss, tonalitic (biotite-hornblende-quartz- 
plagioclase), with amphibolite layers and retro- 
gressive metamorphism to greenschist grade. 
CD-P-1-67 Chips of metagray wacke with a poor 
slaty cleavage. Much of the quartz (.15-2.3 mm), 
microcline, and plagioclase (.15 mm) is probably 
relict sedimentary, whereas the magnetite (.07 mm), 
very minor chlorite (.05 mm) and white mica (.06 
mm) are apparently fine-grained metamorphic 
minerals. About 80 percent of the rock is com- 
posed of quartz sand and silt grains. 
CD-T-3-68 Chips of slaty metasiltstone. Con- 
sists of sericite (.03 mm), quartz (.04 mm), albite 
(.03 mm), minor chlorite (.03 mm), very minor 
tourmaline (.04 mm), and hematite. No new growth 
except for the opaques, chlorite, and white mica. 
CD-T-3-81 Chips of somewhat weathered 
sericite phyllite - probably a metamudstone. Con- 
tains chlorite (.06 mm), sericite (.03 mm), quartz 
(. 10 mm), and opaques (.12 mm). Rock has poorly 
developed schistosity. 

CD-T-1-86 Sericite phyllite and metasandstone 
chips consisting of quartz (.3 mm), angular sericite 
(.06 mm), and minor carbonate (.06 mm). 
CD-T-1-87 Weathered phyllitic metasiltstone 
comprised of sericite (.03 mm), quartz (.05-. 10 
mm), weathered chlorite(?), and hematite. 
CD-T-1-88 * Biotite(?)-sericite-chlorite phyllite 
with good schistosity for a metamudstone. Con- 
sists of chlorite (.06 mm), white mica (.2 mm), 
quartz (.12 mm), weathered biotite(?) (.45 mm), 
opaques (.2 mm), and albite with minor secondary 
tourmaline and apatite. 

CD-T-3-XX Chips of weathered sericite phyllite 
- could be a metamudstone. Contains only fine- 
grained quartz (.03 mm) and sericite (.05-. 1 mm). 
CK-OT-1-65 * A few chips of coarse muscovite 
schist consisting of muscovite (.4 mm), quartz (.15 
mm), albite(?) (.1 mm), weathered biotite (1.5 
mm), graphite, and hematite (weathering product). 



This material is probably not as good as that 
examined by Denison, Raveling, and Rouse (1967) 
who described a garnetiferous schist and muscovitic 
quartzite. Their garnetiferous schist assemblage 
included garnet, biotite, quartz, feldspar, alteration 
chlorite and hematite; and their muscovite schist 
assemblage consisted of quartz, muscovite, an- 
dalusite. 

Daniels and Leo, (1985) described a relatively 
coarse-grained quartz- muscovite-biotite stauro- 
lite (tourmaline) schist from this well. 
CK-OT-1-69 * Slide 1 : Chips mostly of single min- 
erals, but enough are present that it is relatively 
certain that the rock is a granite consisting of quartz 
(1.1 mm), microcline (.64 mm), minor sodic pla- 
gioclase (.6 mm), and biotite (.32 mm). 

Slide 2*: Chips are of granitic aplite consisting 
of quartz (.5 mm), microcline (1.4 mm), albite (.15 
mm), biotite (.56 mm), and muscovite (.3 mm) 
which appears to be of igneous origin. Feldspars 
are 85 percent microcline, 15 percent albite. Also, 
one chip of cataclasite. 

CM-OT- 1-53 * Two slides of chips were made to 
evaluate the lithologies reported by Richards ( 1 953). 
Some samples from intervals below our Coastal 
Plain/basement contact contain rare to common 
chips of a weathered, red, silty clastic rock with a 
clay and hematite matrix. This material is consid- 
ered to be downhole contamination from the over- 
lying Cretaceous section. 

Slide 1*: (from the 5,650 to 5,660-foot inter- 
val) Chips of unmetamorphosed diabase and ba- 
salt. Diabase mineralogy is plagioclase (An 70 ) (.7 
mm), clinopyroxene (1.1 mm), magnetite, and pos- 
sible weathered biotite with common carbonate 
alteration. Of the basalt chips, one may have 
microscopic amygdules, and another appears 
variolitic. The variety of grain sizes suggests that 
the contact and interior of a Jurassic dike or sill has 
been drilled, as does the well record, since 
metarhyolite occurs above the diabase interval. 

Slide 2 (from 3,81 0-foot sample interval) Chips 
of a very pale green metarhyolite - this lithology 
first appears in the 2,830-foot sample. Metamor- 
phic minerals include sericite (.03 mm), calcite 



32 



(0.2 mm), and minor chlorite (.03 mm). The relict 
igneous mineralogy includes phenocry sts of quartz 
(.8 mm), albite (.24 mm), and magnetite (.45 mm), 
and rare alkali feldspar (.6 mm) set in a cryptocrys- 
talline groundmass with eutaxitic structure. Much 
of the matrix appears to be devitrified glass. Cleav- 
age is minor, so the rock may just be hydrother- 
mally altered and not regionally metamorphosed. 
CM-OT-1-65 * Whole slide of weathered very fine 
grained crystal tuff (?) - possibly dacite or rhyolite. 
Consists of relict plagioclase (2.0 mm) and meta- 
morphic white mica (.03-.06 mm) with carbonate 
(0.3 mm) and magnetite (.1-.2 mm). Quartz (.24 
mm) is probably mostly relict volcanic, but some is 
metamorphic. Very low grade metamorphism has 
produced a slight phyllitic foliation. 

Denison, Raveling, and Rouse (1967) describe 
a core of rhyolite porphyry tuff with eutaxitic 
structure, relict pumiceous fragments, and a ground 
mass of quartz and sericite. According to these 
authors, "flow-banding" dipped 15 degrees in the 
well. Their Rb/Sr date of 408±40 could date 
metamorphism. 

CN-OT-1-47 * Chips of a granite comprised of 
perthitic microcline phenocry sts (3.8 mm), quartz 
(1.3-2.8 mm), plagioclase (1.5 mm), green-brown 
biotite (.3 mm), white mica (alteration of plagio- 
clase) (.15-.45 mm?), chlorite (altered from bi- 
otite), and minor magnetite (.2 mm). The rock is 
not metamorphosed or deformed. 
CN-T-1-79 * Chips of coarse-grained microcline 
and quartz along with chips of sericite phyllite with 
white mica (.03-.06 mm), graphite, pyrite, rutile, 
minor quartz (.04 mm), and secondary round cal- 
cite (.12-. 18 mm). Rock has S v a phyllitic folia- 
tion, and S 2 , weak spaced cleavage and crenulation 
foliation. Possibly the coarse microcline and quartz 
grains are derived from an overlying Cretaceous 
sandstone? The phyllite is similar to the rocks in 
HT-OT-1-49, LN-T-2-84, LN-T-2-85, and PT-T- 
1-85. 

CR-OT-1-45 * Chips of biotite gneiss - probably a 
deformed plutonic rock or a metamorphosed im- 
mature sandstone. Consists of biotite (0.3-1.4 
mm), quartz (.45-.93 mm), plagioclase (0.6 mm), 



minor chlorite, and opaques (.15 mm). 
CR-OT-1-46 Chips of altered biotite granodior- 
ite(?). Consists of heavily sericitized plagioclase 
(1 mm), chlorite (.45 mm), quartz (.45 mm), biotite 
(.3 mm), magnetite (.45 mm), minor epidote (.15 
mm), and sericite (.02 mm). No potassium feldspar 
occurs in the chips - unless one of the extremely 
sericitized feldspars is potassic. 
CR-OT-2-46 Chips of granite comprised of 
strained quartz (1.4-1.7 mm), perthitic subhedral 
microcline (1.4 mm), plagioclase (An^ 5 ) (.30 mm), 
opaques (.1-.2 mm), and the alteration products 
white mica and chlorite. Minor biotite is seen in 
binocular microscope examination of loose grains, 
but none is present in thin section. 
CR-OT-3-46 * Chips of altered diorite. Consists of 
plagioclase (An 25 35 ) (.45 mm), brownish green 
hornblende (.30 mm), minor quartz (.6 mm), epi- 
dote (.24 mm), chlorite (.2 mm), sericite, and 
magnetite (.07 mm). No foliation is present, so 
secondary minerals could be due to deuteric or 
hydrothermal alteration. 

CR-OT-4-46 Chips of quartz diorite and one grain 
of albite-quartz-microcline aplite. Quartz diorite 
contains plagioclase (0.6-2 mm) (euhedral oscilla- 
tory normal to patchy zoning with andesine core 
and albite rim), biotite (0.3-.8 mm), hornblende (70 
mm), quartz (.15 mm), and opaques (.15 mm). 
CR-OT-5-46 Small chips of granodiorite or quartz 
diorite. Consists of quartz (0.9 mm), plagioclase 
(An 55 ) (1.2 mm), biotite (.3 mm), opaques (.45 
mm), and minor chlorite (.3 mm) and sericite (.2 
mm). 

CR-OT-2-61 Chips of strained granite. Quartz 
(.9 mm) is intergrown with microperthitic ortho- 
clase (.85 mm). Plagioclase (1.1 mm) is exten- 
sively replaced with sericite (.05 mm). The rock 
also contains chlorite (.3 mm) and minor opaques. 
Strain evidence includes wavy extinction in quartz, 
mortar texture, and microfaults. 
CR-OT-3-61 Chips of unaltered biotite granite. 
Consists of quartz (1.4 mm), perthitic microcline 
(2.8 mm), plagioclase (An 20 ) (2.0 mm), biotite (.8 
mm), and minor opaques (.3 mm) with a grain of 
hornblende (1.2 mm). Plagioclase is slightly 



33 



sericitized. 

CR-OT-2-73 * Chips of very fine grained rock 
with very poor schistosity. Contains clinozoisite 
(0.06 mm), sericite (.02 mm), very minor very fine- 
grained quartz, opaques (.05 mm), and rare relict(?) 
plagioclase (.2 mm). Also contains some possible 
altered lapilli and ash. Rare euhedral plagioclase 
suggests a felsic to intermediate composition tuff. 
CR-OT-1-74 Chips of granite; microperthitic 
microcline (1.7 mm), quartz (1.4 mm), albite (1.2 
mm), biotite (.4-1.2 mm), apatite, zircon, minor 
sericite, and no opaques. Quartz is anhedral and 
interstitial between euhedral microcline and albite. 
The rock has no deformation. 
CU-T-2-76 * Chips of unmetamorphosed dia- 
base. Minerals include .45-1.2 mm-long plagio- 
clase laths (An^), clinopyroxene (.3- 1 .0 mm), pos- 
sible (altered) olivine, unidentified opaques (.15- 
.20 mm), magnetite, minor biotite, and very minor 
pyrite. 

DP-OT-1-69 Chips of metamudstone or meta- 
morphosed intermediate volcanic. Contains chlo- 
rite, quartz, sericite, minor albite, and opaques. All 
grains are about .03 mm except for .15-2.0 mm 
opaques. A weak slaty cleavage is present. 
DP-T-1-79 Chips of sericite phyllite, metamor- 
phosed dacitic, or andesitic tuff consisting of fine- 
grained white mica (.2 mm), quartz (.09 mm), 
epidote (.20 mm), relict plagioclase (.3 mm), and 
opaques (.05 mm). The rock has poor schistosity 
and is weathered. 

DP-T-1-82 Chips of biotite schist and quartz- 
ite. Contains biotite (0.20 mm), quartz (.10 mm), 
albite (.10 mm), microcline (.42 mm), minor epi- 
dote, and calcite. Some of the quartz and feldspar 
grains are relict angular sand and silt grains. 
DP-T-2-82 * Slide 1 * : Whole slide from core is a 
biotite schist containing biotite (.6-1.5 mm), epi- 
dote (.2-1.0 mm), minor calcite, quartz (.15-.45 
mm), minor albite, and retrograde chlorite (.6 
mm). Rock is well layered, so protolith was prob- 
ably an immature silty sandstone. 

Slide 2: Chips of layered biotite schist. Biotite 
(2.2 mm) is both syn- and post-tectonic, with 
quartz (.15 mm), epidote, chlorite, and carbonate. 



Protolith may have been a fine-grained sandstone. 
DR-OT-1-46 * Chips of weathered granite from 
the Hatteras Light well. Consists of quartz (0.9- 1 . 1 
mm) with undulatory extinction, potassium feld- 
spar, bent and strain-twinned plagioclase, weath- 
ered biotite somewhat altered to chlorite, and weath- 
ered opaques. 

Daniels and Leo (1985) describe apparently 
fresher material as fine grained, somewhat altered, 
sheared monzogranite with approximately equal 
proportions of quartz, plagioclase (An 37 ), and It- 
feldspar with 5 percent chloritized biotite. 
DR-OT-1-65 * Chips of altered, strained, and frac- 
tured granite. Consists of strained quartz, bent 
plagioclase (1.5 mm), perthitic orthoclase (2.6 mm), 
sericite (.05 mm), chlorite (.9 mm), and opaques 
with mortar texture, stretched quartz, and filled 
fractures. 

Denison, Raveling and Rouse (1967) described 
a core of sheared granite gneiss, with bent perthitic 
microcline, highly strained quartz, bent and shat- 
tered plagioclase heavily altered to sericite, bent 
biotite, iron oxide, leucoxene, apatite, and zircon. 
Shears dip 45 degrees and grain size ranges up to 1 
cm or more. 

DR-OT-2-65 * Chips of highly weathered interme- 
diate metaplutonic rock with plagioclase, chlorite, 
white mica, weathered biotite(?), quartz, and 
opaques. 

Denison, Raveling, and Rouse (1967) describes 
diabase with red-brown biotite from this well and 
Daniels and Leo (1985) list the basement rock here 
rock as a lamprophyre, but do not describe it. 
DR-OT-3-65 Whole slide from core. The rock 
consists of plagioclase (An 45 ) (0. 1 -.2 mm), carbon- 
ate (.3 mm), chlorite (.05-. 1 mm), and magnetite 
with ilmenite exsolution. Possible origins include 
alteration of a volcanic rock, or hydrothermal alter- 
ation of a gabbro. 

Denison, Raveling, and Rouse (1967) described 
a "carbonatized amphibolite," consisting of 
andesine, hornblende, and iron oxides with alter- 
ation products of calcite, micas, and quartz. A K/ 
Ar date on hornblende yielded a minimum age of 
384+8 Ma. 



34 




DR-OT-4-65 * Chips of altered diorite. Contains 
brown hornblende (0.8 mm), plagioclase (An 27 ) (.8 
mm), common magnetite (.15-. 2 mm), minor py- 
rite, actinolite (.9 mm), and chlorite (.3 mm), with 
minor quartz, white mica. Carbonate and epidote 
occur in a tiny vein. Alignment of plagioclase 
looks more like a relict plutonic texture than a 
deformational effect. 

DR-OT-1-71 * Whole thin section from core. 
Unmetambrphosed granite. Contains perthitic or- 
thoclase (3.1 mm), quartz (3.4 mm), plagioclase 
(An 20 with An 5 rims, normal, oscillatory zoning) 
(1.2-3.9 mm), biotite (1.1 mm), and secondary 
white mica (1 .5 mm). Minor magnetite associated 
with the biotite. 

Russell and others (1981) extensively studied 
this core and described it as an almandine + cordi- 
erite + biotite granite. 

Speer (1981) point-counted the rock: quartz 
30.8 percent, alkali feldspar 42.9 percent, plagio- 
clase 22.2 percent, color index 4. 1 . Other minerals 
include biotite, cordierite, almandine, apatite, fluo- 
rite, ilmenite, monazite, sphalerite, tourmaline, 
titanite, uraninite, and zircon. 
DR-OT-2-71 * Whole slide from core. Coarse gran- 
ite with minor strain. Contains quartz (7.3 mm), 
perthitic orthoclase (7.7 mm), sericitized plagio- 
clase (7.7 mm), and biotite (0.64 mm), 50 percent 
of which is altered to chlorite. The quartz has wavy 
extinction; some of the biotite is kinked; there are 
no opaques; and minor leucoxene is present. 
DR-OT-1-73 Chips of alkali feldspar granite. 
Contains quartz (1 .5 mm), perthitic microcline (2.2 
mm), minor albite (1.2 mm), minor sericite (.46 
mm) alteration, minor opaques (.15 mm), zircon 
(.15 mm), and no biotite. One chip of cataclasite. 
DR-OT-2-73 * Chips of sheared 2-mica granite 
comprised of quartz (.8-1.0 mm), orthoclase (2 
mm), biotite (.7 mm), muscovite (.6 mm), plagio- 
clase (1.0 mm), alteration chlorite, and sericite. 
There are a few shears and quartz strain. Muscovite 
has similar habit to biotite, and does not appear to 
be an alteration product. 

DR-OT-1-74 Chips of granite. Contains perthitic 
microcline (2 mm), quartz (1.2 mm), plagioclase 



(.16 mm), biotite (.5 mm), and minor chlorite (.4 
mm) and white mica (.7 mm). Texture includes 
evidence of minor strain; also a little mortar. Rock 
is very similar to DR-OT-2-74. 
DR-OT-2-74 Chips of strained leucogranite. 
Contains quartz (1.7 mm), very perthitic orthoclase 
(1.1 mm), minor plagioclase, much alteration 
sericite (.02 mm), and no biotite. Feldspars are 
fractured and bent, quartz is strained, and there is 
some mortar texture. 

ED-T-1-82 * Chips of fine-grained foliated 
metasandstone. Contains biotite (.35 mm), musco- 
vite (.1-.3 mm), quartz (.03-. 16 mm), epidote (.3 
mm), chlorite, and minor albite (.2 mm) with a few 
fine grains of magnetite. 

GA-OT-1-71 * Slide 1 * : Chips of very fine-grained, 
non-schistose, intermediate-composition crystal 
meta-tuff, affected by little metamorphism. Con- 
tains epidote, white mica, pyrite, quartz(?), relict 
plagioclase(?) phenocrysts (highly altered), chlo- 
rite, and sphene(?), with a groundmass too fine 
grained to identify optically. 

Slide 2: Chips of fine-grained crystal meta- 
tuff. Contains white mica, epidote, chlorite, pyrite, 
relict plagioclase phenocrysts, and minor zeolites. 

Slide 3: Chips of very low grade, fine-grained 
metavolcanic rock with no schistosity. Consists of 
white mica (.1 mm), chlorite (.1 mm), epidote (.12 
mm), ghosts of relict euhedral plagioclase phenoc- 
rysts (1.5-2 mm), pyrite, possible zeolites, and 
fine-grained unidentified material. 
GR-T-1-68 * Chips of an altered medium-grained 
plutonic rock - probably gabbroic. Most grains are 
of regional metamorphic origin or hydrothermal 
alteration. Minerals present include epidote (.24 
mm), chlorite (.12 mm), magnetite, plagioclase 
(An^ 5 ) (partially relict - 1.2 mm), and rare biotite 
(.1 mm). No schistosity is present. 
GR-T-2-87 * Chips of phyllite comprised of 
sericite (.2-. 3 mm), minor quartz, and goethite 
(weathering extreme). 

HA-A-1-84 * Large chips of metaplutonic rock. 
White mica occurs along extensive shears,. Com- 
mon minerals are quartz (2 mm), altered plagio- 
clase (An 5 ) (2.2 mm), sericitized potassium feld- 



35 



spar, white mica (. 1 mm), chlorite, and magnetite. 
With the feldspars so altered, it is hard to interpret 
the protolith, but the rock must have been in the 
range between granite and granodiorite. Also 
contains microbreccias and, mortar texture 
HA-T-1-85 Chips of sericite phyllite, quartz- 
sericite phyllite, and quartzite. All chips contain 
quartz (.06 mm), sericite (.05-. 1 mm), and hematite 
in varying proportions. Schistosity is mildly crenu- 
lated in the phyllites. Minor epidote (.1 mm) 
occurs in the quartzite. Protolith may have been a 
siltstone. 

HO-P-1-70 * Chips of quartz-sericite phyllite, 
containing quartz (.1-.15 mm), sericite (.07 mm), 
and opaques (.05 mm) (apparently mostly hema- 
tite?) with very minor chlorite. Also some chips of 
fine-grained quartzite. Protolith is probably a 
metasiltstone. 

HR-A-4-83 * Small chips of muscovite phyllite 
and rutilated quartz consisting of muscovite (.5 
mm), minor quartz, and opaques. Foliation is 
slightly crenulated. 

HT-OT-1-49 * Chips of calcareous biotite phyllite. 
Rock is entirely recry stallized. Regional metamor- 
phic minerals are biotite (.3 mm), white mica (.24 
mm), epidote (.25 mm), carbonate (.4 mm), quartz 
(.12 mm), magnetite, and minor untwinned plagio- 
clase. Protolith could be a calcareous gray wacke or 
an altered volcanic rock. Foliation is not too well 
developed, despite the grain size. 
HY-OT-1-65 * Chips of heavily strained quartz 
(.15-.6 mm) (much with mortar texture), some 
strained microcline, plagioclase, white mica, chlo- 
rite (.07 mm), and minor fine-grained pyrite. Ma- 
terial is very weathered. 

This same basement material was described by 
Denison, Raveling, and Rouse (1967) as a gneissic 
granite with microcline perthite, plagioclase, 
strained quartz, muscovite, biotite, chlorite, zir- 
con, apatite, leucoxene, and minor iron oxides. 

Daniels and Leo (1985) describe the rock as a 
leucogranodiorite or a trondhjemite, containing 
plagioclase (An 32 ), quartz, less than 10 percent K- 
feldspar, and less than percent biotite. 
JO-OT-1-60 * Two chips of very low-grade, fine- 



grained, non-foliated metasediment, consisting of 
quartz (.05 .12 mm), white mica (.02 mm), and 
magnetite. This composition also matches altered 
felsic volcanic rocks in the slate belt of North 
Carolina, so the protolith is unclear. 
LN-T-1-74 * Chips of slightly phyllitic crystal 
meta-tuff. Orthoclase crystals (.4-.7 mm) are relict 
volcanic, as are plagioclase (1.0 mm). There is 
some idiomorphic relict quartz, but most quartz (.6 
mm) and all the epidote is of metamorphic origin. 
Opaques are mostly pyrite with minor magnetite. 
Protolith is probably a rhyolite tuff. Radiating 
grains in possible spherulites suggest devitrifica- 
tion textures. 

LN-T-1-79 Chips of greenstone? All grains are 
fine: chlorite (.06 mm), magnetite (.05-. 12 mm), 
white mica (.25 mm), plagioclase? carbonate? No 
foliation is present, rock is barely metamorphosed, 
and alteration could be purely diagenetic. Contains 
one chip of unmetamorphosed gray-brown mud- 
stone (contamination from uphole?). 
LN-T-2-84 * Chips of siltstone with a very weak 
slaty cleavage. Probably the quartz (.02 mm), 
white mica (.03 mm), and silt-size magnetite are all 
of sedimentary origin. Part of the chlorite appears 
metamorphic, some is probably diagenetic. Lami- 
nations of alternating mudstone and siltstone are 
preserved. 

LN-T-2-85 * Whole thin section from basement 
core is of a somewhat phyllitic, metamorphosed 
crystal-lithic tuff. Much of the rock is very fine 
grained; identifiable minerals are plagioclase (An^) 
(1 .2 mm - relict volcanic), broken relict quartz (.5- 
1.5 mm), white mica (.04 mm), carbonate (.45 
mm), and opaques (.15 mm). Rock is probably a 
metarhyolite. 

LN-T-1-86 * Chips of granite with aplitic texture 
- probably a late dike cutting a pluton. Minerals 
include quartz (.3-. 4 mm), microcline (. 1-.45 mm), 
albite (.1-.2 mm), biotite (.12 mm), and minor 
amounts of the following: plagioclase, hornblende, 
magnetite, chlorite. Exhibits hypidiomorphic tex- 
ture. 

LN-T-2-86 Chips of plutonic rock - probably 
monzonite or granodiorite. Rock is not metamor- 



36 



phosed, and shows just minor deuteric alteration 
which has produced chlorite. The primary igneous 
minerals are oligoclase (1.3-2.2 mm), microcline 
(.3 mm), quartz (1 mm), biotite (2.7 mm), minor 
hornblende (1.3 mm), and accessory titanite and 
pyrite. There is much more plagiocla.se than micro- 
cline and quartz, but not enough sample to accu- 
rately name the rock. 

LN-T-3-86 Chips of crumbled plutonic rock - 
approximated as granodiorite. Mineral grains 
present include plagioclase (An^ 29 ) (1 mm), minor 



protomylonite. (Sample site is within Hollister 
fault zone). Consists of quartz (.01 -.6 mm), plagio- 
clase (.3 mm), chlorite (.07 mm), white mica (.08 
mm), opaques (75 percent magnetite, 25 percent 
pyrite) and minor epidote (.02 mm). The plagio- 
clase and some of the quartz grains are relict. The 
rock seems too crystal-rich for a tuff. 
NA-A-2-84 Chips of granitic rock, apparently 
from the Rocky Mount pluton. Contains quartz (2 
mm), oligoclase (3 mm), microcline (1 grain), 
perthitic orthoclase (3.7 mm), biotite (1 mm), with 



potassium feldspar (.5 mm), biotite (.3-1 mm), minor chlorite and epidote (.15 mm), accessory 



minor quartz (1.2 mm), minor magnetite and py- 
rite. There is sericite alteration of the feldspars. 
LN-T-1-88 * Chips of rhyolite porphyry - prob- 
ably from a dike. Contains microcline (1.2 mm) 
microphenocrysts, plagioclase (1.1 mm) 
microphenocrysts, quartz (.2 mm), opaques (.05 
mm), and minor biotite (.2 mm). 
MO-T-1-83 Three small chips of white-mica 
phyllite consisting of white mica (.4 mm) and 
minor opaques (.1 mm). Foliation is pronounced. 
MO-T-1-86 * Chips of biotite-muscovite schist, 
plus some chips of foliated metagraywacke(?). 
Consists of brown-green biotite (.5 mm), musco- 
vite (.2 mm), quartz (.6 mm), oligoclase (.7-1 mm), 
carbonate, minor magnetite, one pyrite grain, and 
chlorite secondary after biotite. Schistosity is well 
developed. Some plagioclase is subhedral, and 
looks like relict volcanic phenocrysts; however, 
the chips have relict layers or different grain sizes 
and compositions, suggesting a silty to sandy clas- 
tic sedimentary rock. 

MO-T-2-86 * Chips of biotite(?)-sericite phyllite. 
Consists of sericite (.2 mm), brown weathered(?) 
biotite, chlorite (.1 mm), quartz (.1-.2 mm), and 
minor epidote (. 1 mm). 

MO-T-1-88 * Chips of weathered mica schist. 
Consists of white mica (. 1-.8 mm), chlorite, quartz 
(.1-.2 mm), weathered biotite(?) (.2 mm), and he- 
matite from weathering. Schistosity is mildly 
crenulated. 

NA-A-1-84 Chips of metamorphosed, some- 
what sheared volcaniclastic sandstone. Some quartz 
ribbons are present - might be termed 



zircon, apatite. For a map of all of the wells drilled 
in the covered parts of the Rocky Mount pluton, see 
Moncla(1990). 

NH-OT-1-66 * Chips of two rock types. One type 
is a slightly phyllitic quartz- sericite rock, possibly 
a metamorphosed felsic volcanic rock, and the 
other is a fine-grained, non-foliated metabasalt. 
The phyllite contains quartz (.01 -.06 mm), and 
fine-grained sericite, albite, hematite, opaques, and 
microcline. Relict laminations indicate a 
metamudstone protolith. The metabasalt contains 
chlorite (.01 -.05 mm), epidote (.06 mm), opaques 
(.04 mm), and titanite. 

NO-T-2-66 Chips of rock mainly consisting of 
strained quartz (.6-1.4 mm), altered plagioclase (.5 
mm), sericitized perthitic orthoclase (.6 mm), 
sericite (.11 mm) with minor epidote (0.25 mm), 
leucoxene, and no opaques. There is poor schis- 
tosity, mortar texture, and one epidote vein. Rock 
could be a deformed granite with quartz veins. 
NO-T-3-66 * Chips of metaplutonic rock, possi- 
bly a granodiorite. Plutonic minerals are plagio- 
clase (1-2 mm), quartz (1.6 mm), and minor 
sericitized potassium feldspar (1 mm), biotite, with 
common epidote (.5 mm) and chlorite(?). There is 
very little magnetite. There is no schistosity, so the 
alteration could be hydrothermal. 
ON-OT-1-50 * Whole slide from core of biotite 
schist - approximately 50 percent of micas are 
parallel to schistosity. Consists of biotite (.45 mm), 
muscovite (.3 mm), quartz (.2 mm), zoned plagio- 
clase (An 023 ) (.7 mm), opaques (mostly pyrite, 
minor magnetite), and retrogressive chlorite. Bi- 



37 



otite is both syn- and post- tectonic. 
ON-OT-1-59 Chips of metasiltstone or possibly a 
felsic metavolcanic with poor slaty cleavage. Rock 
is very fine grained and consists of sericite (.01 
mm), quartz (.06 mm), magnetite (.08 mm), chlo- 
rite (.02 mm), very fine grained albite(?), epi- 
dote(?), and an unidentified ground mass. Rock is 
barely metamorphosed. 

ON-OT-2-59 Chips of sericitic slate - probably 
metadacite. Consists of relict plagioclase phenoc- 
rysts (An^) (.8 mm), sericite (.08 mm), biotite(?) 
(.05 mm), quartz (.04 mm), and minor opaques (. 1 
mm). Rock has two weak cleavages. 
ON-OT-1-60 Chips of felsic metavolcanic rock 
or metasiltstone. Consists of sericite (.01 mm), 
quartz (. 1 mm) and minor plagioclase (. 1 mm) with 
no opaques. There is little foliation. Rock is 
similar to ON-OT-1-59 and ON-OT-2-59. 
ON-OT-2-60 * Chips of phyllitic metavolcanic 
rock, intermediate in composition - probably a 
tuff, but possibly a metagraywacke. Consists of 
quartz (.01-. 1 mm), biotite (.1 mm), white mica 
(.02 mm), epidote (.04 mm), opaques (.05-. 2 mm), 
and unidentified ground mass. 
ON-OT-1-66 Two chips of metarhyolite - prob- 
ably a dike. Grain boundaries are sutured; there is 
a slight schistosity. Rock comprised of quartz (.4 
mm), plagioclase (.3 mm), perthitic microcline 
(.25 mm), minor biotite, sericite, zircon, minor 
chlorite (.3 mm), and minor opaques (.2 mm). 
ON-OT-4-66 Chips of tonalite or granodiorite, 
containing plagioclase (1.5 mm), biotite (2 mm), 
hornblende (1.7 mm), quartz (.46 mm), epidote (.2 
mm), and minor amounts of magnetite, microcline 
(2.8 mm), and chlorite. Rock is somewhat altered, 
possibly due to regional metamorphism. 
ON-OT-1-67 * Slaty metasandstone. Contains 
quartz (.03-. 15 ?), white mica (.01-.09 ?), chlorite 
(.12 mm), and magnetite (.06 mm). Silt and fine 
quartz constitutes 80 percent of the rock. 
ON-OT-2-67 * Intermediate metavolcanic. Rock 
has no schistosity and a very fine grained matrix . 
Consists of plagioclase (.12 mm), chlorite (.12 
mm), epidote (.06 mm), opaques (.05 mm), titanite 
(.06 mm), carbonate (.06 mm), orthoclase(?), and 



quartz (.12 mm) in a vein. 

Daniels and Leo (1985) describe material from 
this hole as quartz-rich metasediment. 
ON-OT-3-67 * Chips of hornblende-biotite-plagio- 
clase "gneiss." Contains hornblende (.7 mm), 
biotite (.36 mm), quartz (.06 mm), andesine (.2 
mm), epidote (.09 mm), magnetite (.2 mm), titanite 
(.2 mm), and minor calcite. There is no schistosity. 
The rock may be a meta-andesite, metatonalite, or 
a mafic inclusion from a pluton. It is of lower 
amphibolite facies. 

ON- T-l-79 Russell and others (198 1) reported 
a clinopyroxene + biotite-bearing amphibole-quartz 
monzonite. 

PA-OT-1-47 * Chips of plutonic rock with slight 
deformation -granodiorite. Consists of bent, strain- 
twinned plagioclase (1-1.2 mm); minor microcline 
(.6 mm); quartz (.8 mm) with undulatory extinction 
and sutured boundaries; kinked, green- brown bi- 
otite (.2 mm); magnetite (1.2 mm); and accessory 
titanite (.5 mm). Some chips of red siltstone as 
contamination. 

PA-OT-2-47 * Chips of foliated, cataclastic, 
metadiorite (protomylonite). Contains hornblende 
(.7 mm), phenocrysts of plagioclase (1.7 mm), 
biotite (.4 mm), fine- grained quartz, sphene (.4 
mm), opaques (.1-.15 mm) (75 percent magnetite, 
25 percent pyrite), and epidote (.3 mm). The fine- 
grained cataclastic groundmass consists of sericite 
(.01 mm), quartz, feldspar, biotite, and epidote. 
PA-OT-3-47 * Chips of fractured sodic 
metagranite. Consists of microcline mesoperthite 
(.9-1.9 mm), microcline/quartz intergrowths, pla- 
gioclase (.3-. 5 mm), polycrystalline quartz (.15 
mm), chlorite (.15 mm), biotite (.15 mm), pyrite 
and magnetite, epidote (.1 mm), and carbonate (.3 
mm) with spray of stilpnomelane. Slight cataclasis 
has given the rock a bimodal grain size in some 
chips. 

PE-OT-1-59 * Chips of mafic metavolcanic rock 
containing chlorite (.06 mm), greenish-brown bi- 
otite(?) (.05 mm), white mica (.03 mm), epidote 
(.06 mm), quartz (.05 mm), apatite, and minor 
opaques (.07 mm). Rock is medium grained, and 
has poor schistosity and no relict igneous textures. 



38 




PE-OT-1-66 * Chips of muscovite granite? Con- 
tains quartz (.3 mm), muscovite (1.2 mm), plagio- 
clase (2.6 mm), biotite (. 1 mm), chlorite (.45 mm), 
and minor opaques. (Poor material, though it is 
clearly undeformed.) 

PE-OT-4-66 Chips of intermediate metavolcanic 
or metagraywacke. Contains chlorite (.05 mm), 
quartz (.15 mm), opaques (.15 mm), epidote (.03 
mm), plagioclase (.2 mm), biotite(?) (.06 mm), and 
sericite (.05 mm). Rock shows no schistosity or 
layering, and has hypidiomorphic texture and su- 
tured grain boundaries. No relict volcanic textures, 
but very low quartz content would be odd in a 
metasediment. 

PE-T-1-83 Described by Daniels and Leo 
(1985) as a biotite-hornblende amphibolite com- 
prised of quartz plus 20 percent plagioclase - a 
metamorphosed mafic volcanic rock at amphibo- 
lite facies. 

PS-OT-1-71 * Chips of diabase and basalt. Con- 
sists of clinopyroxene (.8 mm), plagioclase (.3-.8 
mm), olivine? (weathered) and magnetite (.07 mm), 
with minor very fine-grained pyrite and brown 
spinel (.07 mm). Rock is probably a Jurassic dike 
or sill; the basalt is undoubtedly from the chilled 
contact 

PT-T-1-85 * Whole thin section from core -spot- 
ted metasiltstone, vaguely phyllitic. "Spots" of 
carbonate (.45 mm), quartz (.01-.06 mm) silt grains, 
and white mica (.12 mm), with plagioclase (.06 
mm), minor silt-size magnetite and pyrite; some 
flaky opaques are probably graphite (.01 mm). 
Rock is barely metamorphosed; probably chlorite 
zone or less. Many similarities to BF-OT-4-63 and 
CN-T-1-79. 

PT-T-1-87 * Chips of weathered, altered gran- 
ite. Contains quartz (1.3 mm), perthitic orthoclase 
(1.9 mm), albite (.9 mm), minor chlorite (.15 mm), 
and minor sericite. Rock shows minor mortar 
texture and some wavy extinction in quartz and 
plagioclase. 

RI-T-1-87 * Chips of chlorite- sericite phyllite - 
probably a metamudstone. Contains quartz (.3 
mm), chlorite (.1-.3 mm), sericite (.15 mm), and 
minor opaques. Chips show poor S t and a follow- 



ing crenulation foliation. 

RO-T-2-68 * Chips of sericite phyllite comprised 
of sericite (.03 mm), biotite (.03 mm), quartz (.07 
mm), and opaques (.04 mm). 
RO-T-3-71 Chips of metamudstone. Contains 
sericite, quartz, opaques, possibly graphite, and 
rutile. Rock is very fine grained and 
unmetamorphosed. 

ROT- 1-84 * Chips of sericite slate. Contains 
sericite (.03 mm), quartz (.03 mm), rutile (.01 mm), 
and other fine-grained accessories. Rock has good 
cleavage. 

SA-P-1-67 * Chips of weathered slate. Consists 
of sericite (.03 mm), quartz (. 1 mm), and opaques 
(.03 mm). 

SA-T-1-XX Chips of slaty metamudstone. Con- 
sists of sericite (.02 mm), quartz (.02 mm), magne- 
tite (.03 mm) and graphite. Also contains potas- 
sium feldspar? Rock has no chlorite, is very fine 
grained, and is only very slighdy metamorphosed. 
SA-T-2-84 Chips of slaty metamudstone con- 
sisting of chlorite (.05 mm), white mica (.06 mm), 
quartz (.06 mm), sphene, pyrite (.01 mm), and 
some possible rutile. 

SA-T-1-86 Chips of slightly metamorphosed 
slaty metamudstone. Contains chlorite (.06 mm), 
white mica (.02 mm), quartz (.02- .05 mm), and 
rutile. There is slight grading to laminations; the 
slaty cleavage is at a 90-degree angle to layering. 
TY-OT-1-71 * Chips of phyllite, with a graywacke 
protolith. Contains biotite (.15 mm), chlorite (.15 
mm), oligoclase (.5 mm) with albite rims, white 
mica, microcline perthite, magnetite (.08 mm), 
quartz (.8 mm), carbonate (.1 mm), titanite (.1 
mm), and one grain of epidote. Schistosity is weak 
because of low percentage of micas and the high 
percentage of quartz and plagioclase. 
TY-OT-2-71 * Chips of biotitic medium- to fine- 
grained "gneiss" consisting of biotite (.1-.45 mm), 
white mica (.1 mm), chlorite (.1 mm), quartz (.1- 
.15 mm), magnetite (.1 mm), minor pyrite, altered 
feldspars, minor tourmaline, and carbonate in a 
small vein. Rock is probably a metasandstone. 
Schistosity is relatively well developed. 
VPI-1 Referred to by Becker (1980) as the "Dort 



39 



Granite" and described as a granodiorite consisting 
of oligoclase, microperthitic microcline, quartz, 
biotite, and pargasitic hornblende, with accessory 
titanite, apatite, opaques, zircon, allanite, rutile. 
Alteration products include epidote, chlorite, car- 
bonate, white mica, and myrmekite. The rock was 
reported to have experienced mild deformation, 
producing undulose quartz and minor mortar. 
VPI-2 The basement in the area of this well was 
characterized by Pratt, and others (1985) as lower 
amphibolite-facies layered felsic and mafic 
metavolcanic rocks. 

Becker (1980) reports that the leucocratic lay- 
ers contain the assemblage: quartz + microcline + 
albite + magnetite + phengite + biotite + epidote + 
chlorite + hemo-ilmenite + pyrite + spessartine. 
Mafic layers contain: plagioclase (An 21 ) + epi- 
dote + ilmenite + titanite + biotite + hornblende + 
chlorite + phengite + quartz. 

Russell and Russell ( 1 980) report a Rb/Sr whole 
rock age for the leucocratic crystal tuff of 314+22 
Ma, probably representing an early metamorphic 
age. The rocks reportedly dip 20 to 25 degrees 
roughly to the southeast. 

VPI-3 Core from Rocky Mount pluton described 
by Farrar ( 1 980b) as hornblende-biotite granodior- 
ite, with minor hornblende biotite tonalite and 
biotite granite 

WS-T-1-86 * Chips of metamudstone containing 
quartz (.2 mm), white mica (.15 mm), chlorite (.05 
mm), microcline (.1 mm), and possible highly 
weathered biotite (.3 mm) with no opaques. There 
is some foliation; most of the original sedimentary 
texture is destroyed, but the rock remains lami- 
nated. 

WS-T-2-86 * Chips of white mica schist, quartz- 
white mica schist, and quartzite. Mineralogy is 
quartz (.4 mm) and white mica (.1-.3 ?) with no 
opaques. The protolith could either be a quartz 
sandstone or a hydrothermally leached felsic tuff. 
Several grains are kinked; there is one crenulation 
of schistosity. 

WY-T-1-82 Whole thin section from core of 
metamorphosed tonalite. Consists of plagioclase 
(An 20 ) (1-2.6 mm), quartz (.45 mm), biotite (.1-.45 



mm), chlorite (.12 mm), and clinozoisite (.05 mm) 
with minor sericite. There is a trace of potassium 
feldspar and no opaques. There is also very little 
schistosity. 

WY-T-2-82 * Whole slide from core of 
metatonalite composed of hornblende (. 1 -.45 mm) 
with common overgrowth of actinolite, plagio- 
clase (1.6 mm), quartz (.45 mm), chlorite (.05-. 1 
mm), epidote (.1 mm), and magnetite (.3 mm). 
There is also minor biotite and carbonate in a tiny 
vein with microbreccia. There is no schistosity, so 
all the metamorphism could be hydrothermal. 
WY-T-1-83 * Chips of sericitic slate - fine-grained 
altered felsic metavolcanic or metamudstone. 
Consists of sericite (.005-.01 mm), quartz (.05 
mm), albite (.05 mm), and minor opaques. 
WY-T-1-84 * Chips of fine-grained phyllitic rock 
containing quartz and graphite(?). Rock could be 
either a metamorphosed felsic tuff or a metasiltstone. 
Foliation is heavily crenulated. 
WY-T-3-84 Chips of quartzite and sericite 
phyllite containing quartz (. 14 mm), white mica (. 1 
mm), hematite. Also a chip of metasiltstone with 
relict angular quartz sand grains and slight relict 
bedding. 

WY-T-5-84 * Chips of phyllite comprised of 
quartz (1.55 mm), white mica (.05-. 1 mm), and 
hematite (.03 mm) with two schistosities. The first 
schistosity is heavily folded. 
WY-T-2-86 Chips of phyllitic metavolcanic rock 
with a well-developed schistosity, possibly andes- 
ite. Consists of chlorite (0.1 -.15 mm), plagioclase 
( broken relict phenocrysts) (1.5 mm), white mica 
(.01 mm), quartz (.05-. 1 mm), and magnetite (.03 
mm). 

WY-T-3-86 * Chips of very slightly metamor- 
phosed metavolcanic, approximately a metadacite. 
Contains plagioclase (.8 mm), opaques (.45 mm), 
epidote (.1 mm), and sericite (.02 mm) in a pale, 
very fine-grained groundmass. 
WY-T-4-88 Chips of metabasalt. Consists of 
chlorite (.06 mm), epidote (. 12 mm), rutile, titanite, 
and albitized relict plagioclase (1 mm). Rock 
shows no schistosity. 
WY-T-5-88 * Chips of the following rock types: 



40 



1) carbonate rock - calcite (.3 mm), epidote (.03 opaques (.12 mm), and chlorite; and 4) phyllite - 

mm), plagioclase, white mica (.03 mm), no opaques; sericite (.12 mm), opaques (.15 mm), minor chlo- 

2)quartzite-quartz(.2mm),whitemica(.03mm), rite (.03 mm), quartz (.15 mm), epidote (.06 mm), 

opaques (.08 mm); 3) "mafic rock" - epidote (.20 plagioclase (.2 mm), 
mm), quartz (.03 mm), white mica (.06 mm), 



41 



APPENDIX C - Photomicrographs 
of basement samples 

The following 75 photomicrographs are of 
representative basement samples examined and 
described as part of this study. Many are of thin 
sections made from rock chips picked from well 
cuttings and some are from thin sections made 
from drill cores. The previous section (Appendix 
B) identifies the sample form and provides an 
overall description of the thin section. Whereas 
these samples typically are from the uppermost 
basement rock, most are weathered. 

The well code, polarizer setting, and a scale 
are given directly on the photomicrographs, "xn" 
and "ppl" indicate partially crossed nicols (80° to 
85° between polarizers) and plane polarized light 
settings, respectively. Magnification is either 
47X (0.1 mm-scale) or 1 18X ( 0.2 mm-scale). 




BF-OT-l-63(xn) 



0.1 mm 





BF-OT-4-63 (xn) 



0.2 mm BL-OT-1-59 (ppl) 



0.2 mm 



42 





BL-T-1-81 (xn) 



01mm BL-T-2-84 (xn) 



0.1 mm 





BT-T-1-73 (xn) 



0.1mm BT-T-1-82 (xn) 



0.2 mm 



43 





0-1 mm BW-T-1-73 (xn) 



0.1 mm 




CD-T-1-88 (xn) 



0.2 mm CK-OT-1-65 (xn) 



0.1 mm 



44 





CK-OT-l-69-slide2(xn) 



0.2 mm CM-OT-1-53 - slide 1 (xn) 



0.1 mm 





CM-OT-1-65 (xn) 



0.1mm CN-OT-1-47 (xn) 



0.2 mm 



45 





CN-T-1-79 (ppl) 



0.1 mm CR-OT-1-45 (xn) 



0.1 mm 





CR-OT-3-46 (xn) 



0.1mm CR-OT-2-73 (xn) 



0.1 mm 



46 





'J£. 



CU-T-2-76 (xn) 










r *JPt^k 









01 mm DP-T-2-82 - slide 1 (xn) 



0.1 mm 




DR-OT-1-46 (xn) 



0.2 mm DR-OT-1-65 (xn) 



0.2 mm 



47 








DR-OT-2-65 (xn) 



0.1 mm DR-OT-4-65 (xn) 



0.2 mm 





DR-OT-1-71 (xn) 



0.2 mm DR-OT-2-71 (xn) 



0.2 mm 



48 





DR-OT-2-73 (xn) 



0.2 mm ED-T-1-82 (xn) 



0.1 mm 





GA-OT-1-71 - slide 1 (xn) 



0-2 mm GR-T-1-68 (xn) 



0.1 mm 



49 




GR-T-2-87 (xn) 




HO-P-1-70 (xn) 




0.1mm HA-A-1-84 (xn) 



0.2 mm 




0.1 mm HR-A-4-83 (xn) 
50 



0.1 mm 






HT-OT-1-49 (xn) 



0.1mm HY-OT-1-65 (xn) 



0.1 mm 





JO-OT-1-60 (xn) 



0.1mm LN-T-l-74(xn) 



0.1 mm 



51 




LN-T-2-84 (xn) 




LN-T-l-86(xn) 




LN-T-2-85 (xn) 



0.2 mm 




0.1 mm LN-T-l-88(xn) 
52 



0.1 mm 






MO-T-1-86 (xn) 



0-1 mm MO-T-2-86 (xn) 



0.1 mm 





MO-T-1-88 (xn) 



0-2 mm NH-OT-1-66 (xn) 



0.1 mm 



53 





NO-T-3-66 (xn) 



0.2 mm ON-OT-1-50 (xn) 



0.2 mm 




ON-OT-2-60 (xn) 




0.1 mm ON-OT-1-67 (xn) 



54 





ON-OT-2-67 (xn) 



01mm ON-OT-3-67 (ppl) 



0.2 mm 








PA-OT-l-47 (xn) 



0-1 mm PA-OT-2-47 (xn) 



0.2 mm 



55 





PA-OT-3-47 (xn) 



0.2 mm PE-OT-l-59(ppl) 



0.1 mm 




* 






*^ 






• 

k ' 4 



► 



PE-OT-l-66 (xn) 





0.2 mm PS-OT-1-71 (xn) 



0.1 mm 



56 



£$»;' / 




■■--it • ' '-y 



L 






PT-T-1-85 (xn) 



0.2 mm PT-T-l-87(xn) 



0.2 mm 





RI-T-1-87 (xn) 



0.1 mm RO-T-2-68 (xn) 



0.1 mm 



57 







RO-T-1-84 (xn) 



0.1 mm 





TY-OT-1-71 (xn) 




0-1 mm TY-OT-2-71 (xn) 
58 



0.1 mm 





WS-T-1-86 (xn) 



0.2 mm WS-T-2-86 (xn) 



mf", 

iL ■ ^J^m 

0.1 mm 




# - 

■m *' '" 

Vf. ' 

* ' *' ' ■ V 

• *** 




K* - ** 




. . *s # - 

f;. ■ ' • 1 





WY-T-2-82 (xn) 



0.1mm WY-T-1-83 (xn) 



0.1 mm 



59 



™,m L,BRARY OF NORTH CAROLINA 



3 3091 00582 8066 

10"- ... ,f« 






WY-T-5-84 (xn) 



0.1 mm 



•**. % y 


wr^Ff 


f 




%, * 






f ! *v 


•*< 


W 1 


i 




* * f 






• 


%X* 


a 


. 


^ 


■ V 
1 » 

t : 


4^ 




WY-T-3-86 (xn) 



0.1 mm WY-T-5-88 (xn) 



0.1 mm 



60